BFG platform support is really very good at this point. The latest release of BFG (1.2a11) supports the following platforms:

• UNIX (CPython)
• Windows (CPython)
• Google App Engine
• Jython

I haven't tried it on PyPy. If someone has the gumption to try it out and help out a bit when it breaks, I'll try to make it work on PyPy too.

The reason we can support these platforms: BFG's dependency set is tiny. It's reasonably easy to make them all work on arbitrary platforms. Less software really is an asset.