Natron is a free open-source compositing software for Linux, Windows and Mac OS. It is released under GPLv2 license. It supports EXR, DPX, TIFF, PSD, SVG, RAW, JPG, PNG and more file formats. It supports OpenFX and many free and commercial OpenFX plugins like OpenFX-IO, OpenFX-Misc, OpenFX-Arena, OpenFX-OpenCV, OpenFX-Yadif deinterlacer, OpenFX-Vegas SDK samples, RevisionFX, NeatVideo denoiser, Furnace, KeyLight, GenArts Sapphire and Universe. You can use natron as a command-line tool.
It comes with Retina screen support, optimised multi-threaded rendering pipeline and proxy rendering. you can render multiple graphs at the same time. You can also integrate Natron on a render farm manager.
Some other features are Real-time playback, Motion editing, Multi-view workflow, Rotoscoping and Rotopainting, Tracker node, Nodes presets, embeded Python interpreter
and a Multi-plane workspace.
It is one of the best open source alternative for Adobe After Effects.