My GPU was feeling underused so I created an app which captures an area of the screen and through a range of glsl shaders provides realtime post processing functionality. The video capture shaved about 7 fps of the normal running speed and I normally get a consistent 25fps.
Along with handling syphon input, the app also uses the ofxImageSequenceRecorder add-on to output image sequences.
I have been using this for a while now and for some instances I've managed to provide a client a set of images and animations without even pressing the C4D render button and not going through after effects, it isn't going to replace anything any time soon but for certain things it's really handy.
I started from the open frameworks shader tutorial which uses openGL3 and pretty much all shader references I found have been in openGL2 so everything has been rewritten or converted to #version 150.
Thanks to Vincent Rebers for the screen capture code and to Neil Mendoza for a great set of shaders to learn from amongst other contributors in the OF and openGL community.