https://github.com/roxlu/ofxGLM
This allows 3d models to be imported. For any project that requires a 3d world or 3d models it would be necessary. I tried writing a c++ .obj loader once, it wasn’t fun.
 

https://github.com/egradman/ofxNetworkArduino
ARDWINOO
If I’m feeling rebellious and want to take a project into the 3rd dimension. Servos, sensors, led arrays all become available.

https://github.com/kikko/ofxEmbree 
A raytracing engine lib ray. Allows pretty models —> pretty pictures. Rendering has been the part of the 3d pipeline I have given the least interest. Exploring methods of computational rendering could be fun.