FLAC stands for Free Lossless Audio Codec, an audio format similar to MP3, but lossless, meaning that audio is compressed in FLAC without any loss in quality.
OptimFROG Lossless Audio Compression
Audacity is free, open source software for recording and editing sounds. It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems.
XMPlay
Billy
Foobar2000
Evil Player
Songbird
Vibe Streamer is a free MP3 streaming server that allows you to connect and stream your music using only a standard web browser. - Play your music anywhere!
Duplicate Music Files Finder can track your music files duplicates and delete them. The program uses advanced search techniques to detect duplicates(it searches MP3s TAGS, detects duplicates even if the file names are not the same etc). If duplicates are found you can delete the files you want: just check them and press the right mouse button. You can also play the selected files in your favourite Media Player to see if they really are duplicates.