Quod Libet is a Gapless GTK+-based audio player written in Python. Its designed around the idea that you know how to organize your music better than we do. It lets you make playlists based on regular expressions (dont worry, regular searches work too).
Winyl is a free digital audio player and music library application for organizing and playing audio on Windows.Discontinued
No updates since late 2018
Song Director is a program that plays and keeps track of all your music files. Easier to use and understand than iTunes or Windows Media Player. It unleashes the full power of a modern database system in an extremely simple, easy to use manner.