{ofxPd by Dan Wilcox}

The ofxPd addon could be very helpful if you’re a Pure Data user and feeling more comfortable using Pure Data with sound related manipulation or prefer PD’s sound engine. It enables us to build patches in Pure Data and then directly use them in openFrameworks.

{ofxMSAPhysics by Memo}

A handy addon that simulate basic physics such as springs, attractors and collision. It could be very handy if you’re dealing with animations. It’s always fun to simulate “real-worldish” things in virtual environment and interact with them in the real world..

Also, he has a great fluid addon –ofxMSAFluid and music tempo detector ofxBPMTapper.

{ofxBackground – by JGL}

An openFrameworks addon to show several different methods of using openCV for foreground/background image segmentation

If you’re doing a project that would involve real-time cam streaming and needs to capture motions, I think that’s the very addon you want to try out. By tweaking thresholds and carefully choosing background, there’re many interaction possibilities..