ProCamTookit
Although not exactly a ofxAddon, ProCamToolkit is collection of apps aimed at making high level projector-camera calibration more accessible. What I like about it is the possibility to combine and calibrate multiple cameras and projectors, something I have been wanting to experiment lately. It has been developed by Kyle McDonald during Guest Research Project v.1 at YCAM Interlab.
Github: https://github.com/YCAMInterlab/ProCamToolkit
ofxTimeline
I just can’t say enough good things about James George and his contribution to the Openframeworks community. ofxTimeline is probably one of my favourite addons, espcially when I am dealing and experimenting with generative animations and art. For example the video below is an animation I created with Openframeworks, where all the scaling, rotation, coloring has been automated using timelines.