The biggest addon in there is forked-daapd, which works pretty well for multi-room audio setups.
To go with it, Raspotify is a spotify-connect compatible daemon which can output to either a speaker connected to your device, or to a pipe to work with forked-daapd, allowing you to make a multi-room spotify player.
I also have radicale in there that I’m using myself for cloudless shared calendars and to-do lists.
I have a half-working shairport-sync addon that I could work on publishing if anyone is interested, but since I’m not going to be using it myself I can’t promess it’ll get a lot of support if I do. Let me know if that would be of use to anyone, that would again be a good fit to use with forked-daapd to make your own airplay devices, but the audio sync doesn’t work very well on raspberry pis unfortunately.
I’m currently using a raspberry pi 2 myself but forked-daapd and raspotify have been tried on most platforms and should work without any issues.