It is cross-platform, small and really useful as a secondary tool.
Blender runs both on Win, OSX and Linux.
And – note this, because it is not something we got used to from commercial apps – the size of the full app is less then 50 MB.
In this size you get 2 built-in rendering engines (the GPU-based Cycles and the Blender Internal), Particle & Hair simulation, Compositor and so on.
It is something unbelievable compared to monsters like Max.