I started making a web page that has a feature matrix of each OS
procedure, showing the differences in features between existing Scheme
implementations.

Here's what it looks like so far:
<https://htmlpreview.github.io/?https://github.com/lassik/scheme-os-survey/blob/master/data.html>

That HTML page is made out of a S-expression file by a simple Racket
script. Repo: <https://github.com/lassik/scheme-os-survey>

I'll try to populate the tables swiftly, but contributions from others
are very welcome.