> I can add a bit more about Gauche, Cyclone, Sagittarius, Guile and
> Gerbil.

Great, would be much appreciated!

> But one thing I think we need to make clear is the bootstrap
> thing. With the exception of chibi and guile, I think on listed
> schemes need the (usually latest) version of their own already
> installed to build.

This is doubtless true. The Gambit section in the guide already mentions
that explicitly, but the others don't. Maybe the topic should be dealt
with at the top of the guide in one place.

> There are also some minor differences between a git clone and a
> tarball. Autotools-based ones, for example, need to run autoreconf or
> similar first.

Good. Also true, and worth pointing out.

Gauche has its own ./DIST script for running autoconf and whatever else
is needed. Maybe some other implementations have one too.

> For non-standard builds like these you may also need to setup
> LD_LIBRARY_PATH and stuff properly, and not only standard ones. Chibi
> needs $CHIBI_MODULE_PATH. I think Gerbil and Gambit need $SOME_HOME
> too...

If they do, it's worth pointing out. I think most of these difficulties
come about if you try to run the Scheme directly from the source
directory where you built it, instead of doing `make install` and then
running it from the install location. IIRC Chibi had a common pitfall
that had to do with this, but I forget what it was. Perhaps that it
tries to use an outdated image file from the system-wide location?

> Links to the the relevant, more detailed guides should be added too,
> even if it's just a README file in the repo. That way if the document
> becomes outdated, people can still help themselves.

Also good. Thanks for contributing to this :)