I'm looking for a free, lightweight application to help me preview mashups, mixes, experiments, etc. with multiple audio tracks. I usually use Audacity to render and save audio projects, but it's a lot of trouble to render a track everytime I'm curious what it would sound like with a certain effect. The type of application I'm asking about in this post would basically just let me import a bunch of tracks, apply some minor special effects (mostly I want independent pitch and tempo adjustment, reverb, and gain), and play everything together.
I have been using Quicktime Player to do this so far. It enables simultaneous track play and independent pitch/tempo changing, but it's not ideal because each audio file opens in a separate window with separate controls. I've also tried Qlab, which doesn't seem to have any audio effects other than basic level adjustments. UltraMixer is okay but only allows two tracks at once and doesn't have much in the way of effects.