Can I use a Mac Mini as an Airplay audio receiver?
Proprietary:


AirServer - audio and streaming, Mac/Windows, $15
Reflector - audio and streaming, Mac/Windows/Android, $15
AirFoil - audio only, Mac/Windows/Linux, $30 for Mac/Win, $40 for both, free for linux


Open Source:


casualShare audio and streaming, Java + NodeJS, open source
AirStream (Ruby) - audio and streaming, source only
Kodi - formerly XBMC, audio and streaming, Mac/Windows/Linux+, open source
Shairport Sync - audio only (multi-room), source only (C/make); this is the not-dead version of Shairport


Dead:


AirPlay for Totem - audio and streaming
AirMac, on GitHub - audio and streaming, source only (Objective-C)
AirStream (C#) - audio and streaming, source only
Shairport - audio only, source only (C/make + perl)
Banana TV audio and streaming, Mac, free, but only supports iOS 4.2 through 4.3.5