This is pretty amazing. Auria is a DAW (Digital Audio Workstation) for your iPad that can record and play back up to 48 tracks (24 on a first-gen iPad). It also has a mixer complete with aux sends and sub-groups.
The software even allows you to import your individual audio stems from any of the major DAWs you use and work within your iPad. From there, you can send the stems back into your main DAW when done. Very cool.
Some of the basic effects are included as well, and more can be purchased in-app. Particularly noteworthy is the fact that WaveMachine Labs is working closely with makers of popular plugins in order to make them available for Auria. This can end up becoming an all-in-one studio with the right support.
Check it out here, or see it on the App Store: