Rating of apps keeps coming up, but nobody can decide how rating should work. I'm making this issue to suggest a popularity contest, an opt-in feature of F-Droid to share the list of installed apps to the server, so that the client could show how many users have a certain app installed and possibly sort it by user count in "Most popular" (to add to the categories list, probably below Recently Updated, who knows). This is vaguely based on an old IRC discussion.
The user count should be kept vague, as we will obviously only register part of the amount of users, perhaps just using some "progress bar" with the most popular app filling it 100%, and other apps filling it a percentage of that based on their active installs compared to the most popular app.
This is vaguely related to #53, but also not really, as a popularity contest and app rating can both exist (Google Play does both as well, but requires users to participate).