
Isadora is an interactive video processing system with a graphical user interface. The user interface presents a toolbox of relatively high-level objects ("actors"), and isn't really amenable to the kind of programming design one would find in Jitter. As a result, I initially found Isadora rather hard to get into - somewhat hit-and-miss in terms of selecting the appropriate high-level object to use, and somewhat frustrating when looking for something that Isadora doesn't actually provide. However, it is possible to put together some pleasantly surprising processing effects which don't betray their components, and it is extremely easy to use.
Isadora is OSC-controllable, so if I'm not using Jitter I'll build something in Isadora and then control it from MaxMSP (using fader box, joystick, audio, whatever).