As already mentioned, you’re probably looking for Obtanium. There’s also APKUpdater, which hasn’t seen updates in two years but has a 3.0 branch ready for testing. (I haven’t personally used it.)

For Liftoff specifically, I’ll add that it’s available in the IzzyOnDroid repository for F-Droid, which is useful if you’re already using F-Droid for anything else.

Thanks! I did consider Matrix as well, and in fact just set up a personal server yesterday. I was worried about it being too high of a barrier to entry (the reason I stayed away from my first instinct, IRC…). At least Zulip is intuitively just a chat app, even though it might turn people away who don’t want to register for yet another account. One option could be to add Matrix and IRC bridges for Zulip, in the hopes of keeping everyone happy?

I’m still not sure what the best way forward is. It’s a tricky balance between promoting FOSS and remaining widely familiar.

This is aptly timed for me—I spent some time this weekend trying to decide what chat service to use for a project of mine. I’m just starting to try building the community, so it feels like I should have a chat ready if/when people start showing up.

I didn’t consider Discord because I wanted to stick with free software, for the reasons outlined in this post and other similar ones. In the end, I settled on Zulip, but would be happy to reconsider (so far, the chat is just me talking to myself!) if anyone wants to suggest an alternative or has experience in a similar situation.