Packaging https://traewelldroid.de/ would be great. It is an app for checking-in into (mostly German) trains as a social way of connecting to other people and scoring points etc. Kind of a social platform but very focused (and without chat currently).
The author already provides a FOSSbuild version as an apk on GitHub: Release v2.0.3 · Traewelldroid/traewelldroid · GitHub
The author is not opposed to inclusion, but just has no time: Release on F-Droid · Issue #36 · Traewelldroid/traewelldroid · GitHub