Jitter is the visual half of Max: video frames as matrices, OpenGL worlds as patchable objects, everything processable at signal rate alongside the audio. Since 2002 it has been the environment where patching-minded artists build video instruments.
Its strengths are integration and openness: any audio analysis in the patch drives any visual property, cameras and files and shaders mix freely, and the result can perform inside Ableton via Max for Live. Vsynth, the modular video synth package, is Jitter culture distilled.
The cost is that everything is possible and nothing is finished: Jitter hands you the parts. Tools like Photism take the opposite bet, shipping finished scenes with taste applied.