It builds under Mingw32 as well, and at least an earlier version built with VC++ without modification (I don't have access to a windows machine right now to verify). It also builds under Plan 9, which uses a very old and basic C compiler very far from C99.

Some of the optional extension libraries like networking may not work out of the box, but TinyScheme doesn't have these anyway.

Basically, Chibi was designed as a better TinyScheme. It's just as small, can also easily be included statically without a library, has a nicer (optional) FFI, various features like full Unicode, full numeric tower and hygienic macros (all optional), and is an order of magnitude faster.