This might be a long shot but I thought I'd throw this on here. Natron is a node compositor similar to Adobe After Effects, The Foundry's Nuke and Eyeon's Fusion. I've yet to try it because I usually work on After Effects. However, since I can't take After Effects with me everywhere I go, I might just switch over one project to this and see how it goes portable.
Binary Downloads here:
Source Download here:
The only downside I see is that it "might" require Microsoft's Redistributable should installing error's out on missing DLLs.