diff --git a/salt/salt/consumers/init.sls b/salt/salt/consumers/init.sls
index d1b4bd2..a05a680 100644
--- a/salt/salt/consumers/init.sls
+++ b/salt/salt/consumers/init.sls
@@ -1,3 +1,11 @@
+/etc/systemd/system/consumer-topic_interesting_activity_updater.service:
+  file.managed:
+    - source: salt://consumers/topic_interesting_activity_updater.service.jinja2
+    - template: jinja
+    - user: root
+    - group: root
+    - mode: 644
+
 /etc/systemd/system/consumer-topic_metadata_generator.service:
   file.managed:
     - source: salt://consumers/topic_metadata_generator.service.jinja2
@@ -14,6 +22,10 @@
     - group: root
     - mode: 644
 
+consumer-topic_interesting_activity_updater.service:
+  service.running:
+    - enable: True
+
 consumer-topic_metadata_generator.service:
   service.running:
     - enable: True
diff --git a/salt/salt/consumers/topic_interesting_activity_updater.service.jinja2 b/salt/salt/consumers/topic_interesting_activity_updater.service.jinja2
new file mode 100644
index 0000000..050ab6c
--- /dev/null
+++ b/salt/salt/consumers/topic_interesting_activity_updater.service.jinja2
@@ -0,0 +1,16 @@
+{% from 'common.jinja2' import app_dir, bin_dir -%}
+[Unit]
+Description=Topic Interesting Activity Updater (Queue Consumer)
+Requires=rabbitmq-server.service
+After=rabbitmq-server.service
+PartOf=rabbitmq-server.service
+
+[Service]
+WorkingDirectory={{ app_dir }}/consumers
+Environment="INI_FILE={{ app_dir }}/{{ pillar['ini_file'] }}"
+ExecStart={{ bin_dir }}/python topic_interesting_activity_updater.py
+Restart=always
+RestartSec=5
+
+[Install]
+WantedBy=multi-user.target
diff --git a/tildes/alembic/versions/cddd7d7ed0ea_add_interesting_activity_topic_sorting.py b/tildes/alembic/versions/cddd7d7ed0ea_add_interesting_activity_topic_sorting.py
new file mode 100644
index 0000000..b51c0e1
--- /dev/null
+++ b/tildes/alembic/versions/cddd7d7ed0ea_add_interesting_activity_topic_sorting.py
@@ -0,0 +1,101 @@
+"""Add "interesting activity" topic sorting
+
+Revision ID: cddd7d7ed0ea
+Revises: a2fda5d4e058
+Create Date: 2019-06-10 20:20:58.652760
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = "cddd7d7ed0ea"
+down_revision = "a2fda5d4e058"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.add_column(
+        "topics",
+        sa.Column(
+            "last_interesting_activity_time",
+            sa.TIMESTAMP(timezone=True),
+            server_default=sa.text("NOW()"),
+            nullable=False,
+        ),
+    )
+    op.create_index(
+        op.f("ix_topics_last_interesting_activity_time"),
+        "topics",
+        ["last_interesting_activity_time"],
+        unique=False,
+    )
+
+    op.execute("UPDATE topics SET last_interesting_activity_time = last_activity_time")
+
+    op.execute(
+        """
+        CREATE TRIGGER send_rabbitmq_message_for_comment_delete
+            AFTER UPDATE ON comments
+            FOR EACH ROW
+            WHEN (OLD.is_deleted = false AND NEW.is_deleted = true)
+            EXECUTE PROCEDURE send_rabbitmq_message_for_comment('deleted');
+
+
+        CREATE TRIGGER send_rabbitmq_message_for_comment_undelete
+            AFTER UPDATE ON comments
+            FOR EACH ROW
+            WHEN (OLD.is_deleted = true AND NEW.is_deleted = false)
+            EXECUTE PROCEDURE send_rabbitmq_message_for_comment('undeleted');
+
+
+        CREATE TRIGGER send_rabbitmq_message_for_comment_remove
+            AFTER UPDATE ON comments
+            FOR EACH ROW
+            WHEN (OLD.is_removed = false AND NEW.is_removed = true)
+            EXECUTE PROCEDURE send_rabbitmq_message_for_comment('removed');
+
+
+        CREATE TRIGGER send_rabbitmq_message_for_comment_unremove
+            AFTER UPDATE ON comments
+            FOR EACH ROW
+            WHEN (OLD.is_removed = true AND NEW.is_removed = false)
+            EXECUTE PROCEDURE send_rabbitmq_message_for_comment('unremoved');
+
+
+        CREATE TRIGGER send_rabbitmq_message_for_comment_label_delete
+            AFTER DELETE ON comment_labels
+            FOR EACH ROW
+            EXECUTE PROCEDURE send_rabbitmq_message_for_comment_label('deleted');
+    """
+    )
+
+    # manually commit before disabling the transaction for ALTER TYPE
+    op.execute("COMMIT")
+
+    # ALTER TYPE doesn't work from inside a transaction, disable it
+    connection = None
+    if not op.get_context().as_sql:
+        connection = op.get_bind()
+        connection.execution_options(isolation_level="AUTOCOMMIT")
+
+    op.execute("ALTER TYPE topicsortoption ADD VALUE IF NOT EXISTS 'ALL_ACTIVITY'")
+
+    # re-activate the transaction for any future migrations
+    if connection is not None:
+        connection.execution_options(isolation_level="READ_COMMITTED")
+
+
+def downgrade():
+    op.execute(
+        "DROP TRIGGER send_rabbitmq_message_for_comment_label_delete ON comment_labels"
+    )
+    op.execute("DROP TRIGGER send_rabbitmq_message_for_comment_unremove ON comments")
+    op.execute("DROP TRIGGER send_rabbitmq_message_for_comment_remove ON comments")
+    op.execute("DROP TRIGGER send_rabbitmq_message_for_comment_undelete ON comments")
+    op.execute("DROP TRIGGER send_rabbitmq_message_for_comment_delete ON comments")
+
+    op.drop_index(op.f("ix_topics_last_interesting_activity_time"), table_name="topics")
+    op.drop_column("topics", "last_interesting_activity_time")
diff --git a/tildes/consumers/topic_interesting_activity_updater.py b/tildes/consumers/topic_interesting_activity_updater.py
new file mode 100644
index 0000000..aadc890
--- /dev/null
+++ b/tildes/consumers/topic_interesting_activity_updater.py
@@ -0,0 +1,88 @@
+# Copyright (c) 2019 Tildes contributors <code@tildes.net>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+"""Consumer that updates topics' last_interesting_activity_time."""
+
+from datetime import datetime
+from typing import Optional
+
+from amqpy import Message
+
+from tildes.enums import CommentTreeSortOption
+from tildes.lib.amqp import PgsqlQueueConsumer
+from tildes.models.comment import Comment, CommentInTree, CommentTree
+
+
+class TopicInterestingActivityUpdater(PgsqlQueueConsumer):
+    """Consumer that updates topics' last_interesting_activity_time."""
+
+    def run(self, msg: Message) -> None:
+        """Process a delivered message."""
+        trigger_comment = (
+            self.db_session.query(Comment)
+            .filter_by(comment_id=msg.body["comment_id"])
+            .one()
+        )
+
+        topic = trigger_comment.topic
+
+        all_comments = self.db_session.query(Comment).filter_by(topic=topic).all()
+
+        tree = CommentTree(all_comments, CommentTreeSortOption.NEWEST)
+
+        # default the last interesting time to the topic's creation
+        last_interesting_time = topic.created_time
+
+        for comment in tree:
+            branch_time = self._find_last_interesting_time(comment)
+            if branch_time and branch_time > last_interesting_time:
+                last_interesting_time = branch_time
+
+        topic.last_interesting_activity_time = last_interesting_time
+
+    def _find_last_interesting_time(self, comment: CommentInTree) -> Optional[datetime]:
+        """Recursively find the last "interesting" time from a comment and replies."""
+        # if the comment has one of these labels, don't look any deeper down this branch
+        uninteresting_labels = ("noise", "offtopic", "malice")
+        if any(comment.is_label_active(label) for label in uninteresting_labels):
+            return None
+
+        # the comment itself isn't interesting if it's deleted or removed, but one of
+        # its children still could be, so we still want to keep recursing under it
+        if not (comment.is_deleted or comment.is_removed):
+            comment_time = comment.created_time
+        else:
+            comment_time = None
+
+        # find the max interesting time from all of this comment's replies
+        if comment.replies:
+            reply_time = max(
+                [self._find_last_interesting_time(reply) for reply in comment.replies]
+            )
+        else:
+            reply_time = None
+
+        # disregard either time if it's None (or both)
+        potential_times = [time for time in (comment_time, reply_time) if time]
+
+        if potential_times:
+            return max(potential_times)
+
+        # will only be reached if both the comment and reply times were None
+        return None
+
+
+if __name__ == "__main__":
+    TopicInterestingActivityUpdater(
+        queue_name="topic_interesting_activity_updater.q",
+        routing_keys=[
+            "comment.created",
+            "comment.deleted",
+            "comment.edited",
+            "comment.removed",
+            "comment.undeleted",
+            "comment.unremoved",
+            "comment_label.created",
+            "comment_label.deleted",
+        ],
+    ).consume_queue()
diff --git a/tildes/sql/init/triggers/comment_labels/rabbitmq.sql b/tildes/sql/init/triggers/comment_labels/rabbitmq.sql
index aac5f04..7e48c38 100644
--- a/tildes/sql/init/triggers/comment_labels/rabbitmq.sql
+++ b/tildes/sql/init/triggers/comment_labels/rabbitmq.sql
@@ -28,3 +28,9 @@ CREATE TRIGGER send_rabbitmq_message_for_comment_label_insert
     AFTER INSERT ON comment_labels
     FOR EACH ROW
     EXECUTE PROCEDURE send_rabbitmq_message_for_comment_label('created');
+
+
+CREATE TRIGGER send_rabbitmq_message_for_comment_label_delete
+    AFTER DELETE ON comment_labels
+    FOR EACH ROW
+    EXECUTE PROCEDURE send_rabbitmq_message_for_comment_label('deleted');
diff --git a/tildes/sql/init/triggers/comments/rabbitmq.sql b/tildes/sql/init/triggers/comments/rabbitmq.sql
index 457ed1a..2d626b8 100644
--- a/tildes/sql/init/triggers/comments/rabbitmq.sql
+++ b/tildes/sql/init/triggers/comments/rabbitmq.sql
@@ -32,3 +32,31 @@ CREATE TRIGGER send_rabbitmq_message_for_comment_edit
     FOR EACH ROW
     WHEN (OLD.markdown IS DISTINCT FROM NEW.markdown)
     EXECUTE PROCEDURE send_rabbitmq_message_for_comment('edited');
+
+
+CREATE TRIGGER send_rabbitmq_message_for_comment_delete
+    AFTER UPDATE ON comments
+    FOR EACH ROW
+    WHEN (OLD.is_deleted = false AND NEW.is_deleted = true)
+    EXECUTE PROCEDURE send_rabbitmq_message_for_comment('deleted');
+
+
+CREATE TRIGGER send_rabbitmq_message_for_comment_undelete
+    AFTER UPDATE ON comments
+    FOR EACH ROW
+    WHEN (OLD.is_deleted = true AND NEW.is_deleted = false)
+    EXECUTE PROCEDURE send_rabbitmq_message_for_comment('undeleted');
+
+
+CREATE TRIGGER send_rabbitmq_message_for_comment_remove
+    AFTER UPDATE ON comments
+    FOR EACH ROW
+    WHEN (OLD.is_removed = false AND NEW.is_removed = true)
+    EXECUTE PROCEDURE send_rabbitmq_message_for_comment('removed');
+
+
+CREATE TRIGGER send_rabbitmq_message_for_comment_unremove
+    AFTER UPDATE ON comments
+    FOR EACH ROW
+    WHEN (OLD.is_removed = true AND NEW.is_removed = false)
+    EXECUTE PROCEDURE send_rabbitmq_message_for_comment('unremoved');
diff --git a/tildes/tildes/enums.py b/tildes/tildes/enums.py
index fda19bd..862ba61 100644
--- a/tildes/tildes/enums.py
+++ b/tildes/tildes/enums.py
@@ -117,12 +117,28 @@ class ScraperType(enum.Enum):
 
 
 class TopicSortOption(enum.Enum):
-    """Enum for the different methods topics can be sorted by."""
+    """Enum for the different methods topics can be sorted by.
+
+    Note that there are two sort methods based on activity:
+      - "All activity" will bump a topic back to the top of the sort whenever *any* new
+        comments are posted in that topic, similar to how forums behave. This uses the
+        Topic.last_activity_time value.
+      - "Activity" tries to only bump topics back up when "interesting" activity
+        occurs in them, using some checks to decide whether specific comments should be
+        disregarded. This uses the topic.last_interesting_activity_time value, which is
+        updated by a separate background process (topic_interesting_activity_updater).
+    """
 
+    ACTIVITY = enum.auto()
     VOTES = enum.auto()
     COMMENTS = enum.auto()
     NEW = enum.auto()
-    ACTIVITY = enum.auto()
+    ALL_ACTIVITY = enum.auto()
+
+    @property
+    def display_name(self) -> str:
+        """Return the sort method's name in a format more suitable for display."""
+        return self.name.capitalize().replace("_", " ")
 
     @property
     def descending_description(self) -> str:
@@ -135,7 +151,9 @@ class TopicSortOption(enum.Enum):
         if self.name == "NEW":
             return "newest"
         elif self.name == "ACTIVITY":
-            return "activity"
+            return "relevant activity"
+        elif self.name == "ALL_ACTIVITY":
+            return "all activity"
 
         return "most {}".format(self.name.lower())
 
diff --git a/tildes/tildes/models/comment/__init__.py b/tildes/tildes/models/comment/__init__.py
index b9cb436..5871321 100644
--- a/tildes/tildes/models/comment/__init__.py
+++ b/tildes/tildes/models/comment/__init__.py
@@ -6,5 +6,5 @@ from .comment_notification import CommentNotification
 from .comment_notification_query import CommentNotificationQuery
 from .comment_query import CommentQuery
 from .comment_label import CommentLabel
-from .comment_tree import CommentTree
+from .comment_tree import CommentInTree, CommentTree
 from .comment_vote import CommentVote
diff --git a/tildes/tildes/models/topic/topic.py b/tildes/tildes/models/topic/topic.py
index b673c33..1f8119a 100644
--- a/tildes/tildes/models/topic/topic.py
+++ b/tildes/tildes/models/topic/topic.py
@@ -89,6 +89,12 @@ class Topic(DatabaseModel):
         index=True,
         server_default=text("NOW()"),
     )
+    last_interesting_activity_time: datetime = Column(
+        TIMESTAMP(timezone=True),
+        nullable=False,
+        index=True,
+        server_default=text("NOW()"),
+    )
     is_deleted: bool = Column(
         Boolean, nullable=False, server_default="false", index=True
     )
diff --git a/tildes/tildes/models/topic/topic_query.py b/tildes/tildes/models/topic/topic_query.py
index 1c842a2..74ec553 100644
--- a/tildes/tildes/models/topic/topic_query.py
+++ b/tildes/tildes/models/topic/topic_query.py
@@ -126,6 +126,8 @@ class TopicQuery(PaginatedQuery):
         elif sort == TopicSortOption.NEW:
             self._sort_column = Topic.created_time
         elif sort == TopicSortOption.ACTIVITY:
+            self._sort_column = Topic.last_interesting_activity_time
+        elif sort == TopicSortOption.ALL_ACTIVITY:
             self._sort_column = Topic.last_activity_time
 
         self.sort_desc = desc
diff --git a/tildes/tildes/templates/topic_listing.jinja2 b/tildes/tildes/templates/topic_listing.jinja2
index f3703ac..ac8c3bc 100644
--- a/tildes/tildes/templates/topic_listing.jinja2
+++ b/tildes/tildes/templates/topic_listing.jinja2
@@ -36,7 +36,7 @@
       {% endif %}
 
       <a href="{{ request.current_listing_base_url({'order': option.name.lower()}) }}">
-        {{ option.descending_description.capitalize() }}
+        {{ option.display_name }}
       </a>
 
       </li>
diff --git a/tildes/tildes/templates/user.jinja2 b/tildes/tildes/templates/user.jinja2
index 4215d08..407e613 100644
--- a/tildes/tildes/templates/user.jinja2
+++ b/tildes/tildes/templates/user.jinja2
@@ -43,7 +43,7 @@
     <div class="listing-options">
       <menu class="tab tab-listing-order">
         <li class="tab-item{{' active' if not post_type else ''}}">
-          <a href="{{ request.current_listing_normal_url() }}">All activity</a>
+          <a href="{{ request.current_listing_normal_url() }}">All posts</a>
         </li>
         <li class="tab-item{{' active' if post_type == 'topic' else ''}}">
           <a href="{{ request.current_listing_normal_url({'type': 'topic'}) }}">Topics</a>