Mellotron is exactly what the title implies-- a virtual mellotron app. With this, you can load up different instrument files that consist of looping sound files. Your keyboard acts as a piano keyboard, so each letter key on your computer keyboard points to a key on the piano keyboard (if you can wrap your head around THAT).

I actually find myself using this nifty program a lot. It's very good for audio recordings. Also, you can make your own instrument files, since they aren't embedded into the software itself.