A user must choose a primary tag for their post (only admins/moderators can use the "Announcements" tag), and may add 0 or as many as 5 secondary tags. If you take a look at the tag list, you'll see the primary and secondary choices I made so far. Since a post can have at most 5 secondary tags, I tried to stick with things that were either more generic or more likely to have a large user-base. That's why I left off things like "Pebble Tasker" and "Join by joaoapps". Otherwise, I'd be curious to know what I might have missed. I don't know if what I made so far is too much, or if it's not enough, so feel free to critique away.