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.
It depends on what you mean by real world applications, but Chibi has many features including threads, networking and an FFI suitable for any application. R7RS large will have even more libraries. It will be complete when it's completed, but many of the individual libraries will be usable before then.
Chibi is about the same size, and unlike TinyScheme is a real Scheme with hygienic macros and a fast VM (TinyScheme is hopelessly slow). It also has features like Huffman compressed immediate symbols to further reduce runtime heap usage - the raw image size isn't the whole story.
The default heap is 2MB, but will run with 756KB. If you want to skip the init.scm file (-q command-line option) it will run with just 10KB providing only definitions and C primitives, but I haven't tested this extensively - I had no idea they still made devices with such little memory :)
It has no doubt bit-rotted, but had some really
nice features, like being able to automatically
display any file as HTML with the exact same
syntax highlighting that Emacs itself uses.
This is bad a joke - not only the classes and methods but the individual instances have statically generated names. That means in the examples, for the statically generated "one", "two" and "three" there's no way to assign them to another variable, or pass them as arguments to a function.
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.