Its actually useful for creating much more than shaders, but I’ve recently added support for GLSL which I think makes it more interesting for programmers writing GL code for other projects.
here’s a screenshot and movie:
http://treyharrison.com/salvation/screenshots/glsl_fpbuffer.html
download a demo of the software here:
http://www.treyharrison.com/SalvationDemoInstall_110304.exe
the demo does not allow saving or .avi export, but I am still accepting beta tester applications here: