I’ve last seen it last month. And I have an old chat, where FluffyChat and (“old”) Element show all messages by now, but Element X can’t decrypt many and both Elements report that they can’t guarantee the authenticity of many messages (even my own). For a long time, my chat partner could only read messages I sent via FluffyChat but not those sent by Element. I have not checked if that is still the case.

For public transit routing, I usually use the app of the local provider. But especially (not only) for Germany, Öffi is an open source alternative for them, that uses their APIs, I think.

FairEmail, email app for Android that has every feature I can imagine. Available on FDroid

OsmAnd, mobile app for navigation and maps. Offline, based on OSM, can do anything. I use it for checking out and bookmarking places, finding POIs and pubic transport stations, routing (especially for bike and foot), measuring distances, and so on. It can also show and record tracks, do car navigation, edit OSM points, and more stuff that I don’t use. Pro/plus/full version free on FDroid