AIFF

AIFF is usually thought of as the mac equivalent of WAV, but this isn't really fair. It's a lot more complex, and indescribably more abstract and flexible. Like Quicktime, it's more an abstract framework than anything else. AIFF does not dictate Compressor; data can be saved and used lossless, and it usually is, but it is allowed to use literally any compressor you want, including compressors you've defined yourself. (Although obviously, if you define your own compressor or use any compression method less standard than, say, MACE, other programs won't be able to interpret your files..). The coolest part is that you were actually allowed to switch compressors at will at any point in time within the file-- different parts of the sound file could be in totally different formats. The other cool bit was that you could insert blocks of any kind of arbitrary application-specific data you wanted and flag it a certain way, and any other applications would politely ignore the foreign data and even preserve it when editing the file.

AIFF never really caught on as a distribution format on the internet, because Apple never tried to make it catch on in any way, and because windows used WAV, so WAV became standard. Finding an AIFF outside the mac community is very, very rare, although supposedly SGI uses it for some purposes, but when it is it uses the extension .AIF. Within the mac community, though, mac users tend to use AIFF pretty much exclusively for lossless sound data storage, anywhere that windows users would use a WAV. For example, mac cd burners expect to be given any sound files to burn as audio cds in AIFF format, not WAV. Compressed AIFFs are pretty rare these days because, c'mon, we have MPEG.