VLC Media Player - VLC is a free and open source cross-platform multimedia player and framework.
Pennywise - Cross-platform application to open any website or media in a floating window
AIMP - AIMP : Free Audio Player : Официальный сайт программы
PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
foobar2000 - An advanced freeware audio player for the Windows platform.
PiPer - A DIY Minecraft computer to build gadgets