ProLoop is an audio loop playing and sound experimentation app from Trapcode. It features a pretty cool looking interface that shows the waveform of each loop as it plays. It can play up to 6 loops and you can mix and pan each independantly. Where ProLoop shines is it's ability to mangle your loops by repitching them or performing various modulations on them (using other loops as a modulation source). You can also pitch shift loops by musical amounts, and you have control over quantization. It comes bundled with an assortment of strange loops and offers the ability to load your own loops. Other looping apps, such as Looptastic also let you play and mix loops (with an easier interface), but ProLoop should appeal to experimental, ambient, and noise oriented folks who like to play with sounds live.