add "sort threads by" and options to filter threads by tag to the view threads page.
"sort threads by" has options "last activity (newest first)", "last activity (oldest first)", "created (newest first)", "created (oldest first)". forums can also specify have a default sort order for threads in that forum.
not sure how much control the "filter by tag" part needs. a simple "show threads with this one tag and not threads that don't have this tag" (only one tag at a time) would meet most use cases, i think. if not, a more complex "show all threads with any of these tags, don't show threads with any of these tags, don't care about other tags" system (or indeed, arbitrary boolean expressions) could be implemented, though the ui would be trickier and the advantages of this are unclear.
assigned to: no one
fossil branch: thread-filtering