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.

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.