The service, called Myna, is sort of like Garage Band in your web browser. You can import audio directly into it, record a track into the application, or use clips from one of Aviary's provided clip libraries.
All audio effects are non-destructive and you can automate fades and pans, modify gain over time, loop, stretch and reverse audio clips and more. Once you've got your track just the way you want it, you can mixdown to your desktop or publish directly to your Aviary account.
The entire process takes place inside your web browser (Adobe Flash is required) and the interface is both robust and easy to use. Anyone familiar with multi-track audio apps will be familiar with Myna's layout, and I was impressed with the speed of the app. You can playback clips before dragging them to the time line, which is really nice.
Check out this video demonstration:
I've always been opposed to using online audio editing tools, because I haven't found them to be robust or fast enough to be compelling to use. Myna just might change that, because think about how convenient it could be to start a project on one computer and pick it up some place else.