If anyone on this network is interested in compositing VFX work, there is an open source compositor app being developed on the Linux platform and later for the PC. The API for MacOs development has not been planned yet. You can visit the site and see a demo for a Linux alpha release at http://lnkd.in/dVZsnPB. This application she be a free high compositor once in beta release.
I came across a Foundry Nuke inspired open source 2d VFX compositor. The website is at natron.inria.fr. The image below is an screenshot of what the app looks like. It is cross platform with linux, Mac and Windows.