They're Linux based, so anything that will build under Linux and isn't inextricably tied to x86 should work. There's not much in the way of local graphics for them, though, so whatever you use will need to support a remote OpenGL protocol or other remote-3D app.
Your basic Linux ones should be fine: GIMP, Blender, whatever.
As far as proprietary apps, probably not much. You might be able to get some stuff that ran on the Prism to run on Altix if it doesn't require a local GPU.
Altix follows the modern "big machine" concept of them being pretty strictly computational back-ends to PC, Mac, web, or otherwise networked front-ends.