Potentially complicated builds we're still missing:

* Hosted: Kawa and IronScheme
* R6RS compilers: Chez, Ikarus, Vicare, Larceny, Loko
* R6RS interpreters: Petite Chez, Ypsilon, Mosh
* R5RS+: Bigloo, Chicken, MIT Scheme
* Racket (pre- and post-Chez -- is Racket currently a too fast-moving
target for the guide?)

We could gather a separate guide (or a section at the end of the current
guide) for small Schemes that are especially easy to build: the kind
where you run something like "make" and it takes <1 minute from scratch.
S7, S9, FemtoLisp, etc. Those guides can be significantly less detailed
but still nice to have.