As lead of the development, I would like to introduce you to a new cross-platform and open-source nodal compositing software: Natron .
Natron is 100% OpenFX v1.3 compatible , you can see a non exhaustive list of most of existing plug-ins here .
This means most compositing tools such as Sapphire from Genarts or Furnace by the Foundry work totally in Natron. You’re not a commercial plug-ins fan ? Fine ! Many open-source OpenFX plug-ins exist, notably the major suite TuttleOFX.
Also Natron uses many other open-sources projects in order to provide the end-user some flexibility: OpenColorIO for colour management and OpenImageIO for image reading/writing.
For now, 32/64 bits build are available for MacOSX (>= 10.6) and Windows 64 bits (32 bits coming soon).
Please check it out and give us some feedback on Natron’s Forums or via the mailing list natron at inria dot fr.