This is the git repository, for the hardcore hacker types. If you just want to use MidiTumbler, download it from my website.
It's been built for Windows and OS X succesfully, though it doesn't appear to work under OS X. A Linux port is unlikely.
Setting up a build environment
You'll need a copy of Box2D compiled as a static library, as well as the VST SDK. I set mine up so that in my Visual Studio 2010 folder I have a lib folder, into which I have put the Box2D source and VST SDK, as Box2D_v2.2.1 and vstsdk2.4, respectively. The project file uses relative paths, so you can do the same without having to touch the project properties. Obviously it's easily customisable :-)