1) Nuclear - Desktop music player focused on streaming from free sources (in beta phase):
Nuclear Mastodon account: @nuclear
2) Pidgin - IM with options to add various third party plugins which enables you to use facebook chat, steam chat, etc, XMPP included.
3) Synchting - cross platform peer to peer file synchronization, also available on f-droid:
A Mastodon instance for maths people. The kind of people who make \(\pi z^2 \times a\) jokes.
\) for inline LaTeX, and
\] for display mode.