Openframeworks by Zach Lieberman and Theodore Watson is available for download at http://openframeworks.cc.
A short description from the website: Openframeworks is a c++ library designed to assist the creative process by providing a simple and intuitive framework for experimentation. OpenGL for graphics, rtAudio for audio input and output, freeType for fonts, freeImage for image input and output, quicktime for video playing and sequence grabbing.
