ALAC files are very similar to FLAC files, except with a codec developed by Apple. Like FLAC, the files are compressed in size but still contain the full, original audio quality.
Player Support (only free options listed):
Windows: iTunes, Foobar2000, SongBird, Clementine, MediaMonkey, VLC
Mac: iTunes, SongBird, Clementine
iPhone/iPod/iOS: Native Support (any)
Total Download Size: 219MB