VSXu (VSX Ultra) is an OpenGL-based, modular programming environment with for main purpose, the visualization of music and the creation of graphic effects in real-time. VSXu is free and open source and is available for Windows and Linux.
VSXu Artist: the application that allows you to create scenes and demos. Works with a graphical node-based scene graph. Maybe it’s me or the Intel HD 4600 GPU, but I didn’t manage to see the scene preview (in the top-left window)…
VSXu authors have release a demoscene prod with their tool that ranked #3 at ASM 2011 demo competition. Not bad!