Acid Pro is a Wintel- based program with over 400 music loops. It's made by Sonic Foundry, and is currently in version 2.0. Acid Pro is used by many electronica and techno artists, and even some rap enthusiasts. You can combine loops to create your own and add them to your songs.

Loops are small snippets of songs, such as a part of a guitar solo or a part of a musical phrase. If you're listening to a tune and you recognize the guitar riff, it probably is a sampled loop from an old song.

Acid Pro is not a kiddie tool. It costs $399US list price, but can be found at about $289US in larger stores.