Audiobus 3 is just waiting for Korg Gadget to get it's act together and then it could well have cracked the idea of an iPad as a music workstation
Free guitar amp plugin for Mac and PC which looks very familiar indeed!
Gig Performer is a plug-in host for live performance that lets you create your own multi-touchable front panel controls for your whole rig. Looks dated but the functionality is cutting edge.
You can play your virtual instruments DAW free in this nice, if slightly flaky, vPlayer VST Host from Digital Brain Instruments