I stumbled upon https://github.com/udem-dlteam/libs/ but:
Great. I didn't know it was public :) It's mostly (but not exclusively) SRFIs for now.
A) There is no tests
Work in progress :)
A lot of SRFIs don't have many tests. It might be nice to gather a big, up-to-date test suite for all SRFIs. Or keep up-to-date tests in each SRFI's repo with the sample implementation.
B) There is no doc
All except one of the current ones are SRFI implementations, so the SRFI is the documentation.
C) The layout of the repository is as far as I can tell:
libs/srfi/1/1.sld
That would me that srfi 1 is importable with:
(import (srfi 1 1))
which looks odd. Maybe I misunderstood something.
Gambit's lookup rules allow either foo.sld or foo/foo.sld to be imported with (import (foo)). This may be unusual among R7RS Schemes.
D) There is not (scheme fu) libraries
They are in the lib/scheme directory Gambit's main repo: https://github.com/gambit/gambit/tree/master/lib/scheme
It also has a lib/srfi directory: https://github.com/gambit/gambit/tree/master/lib/srfi
Most of the SRFI implementations from udem-dlteam/libs will probably be merged into Gambit's main repo once they have been tested enough; libs is mostly for work-in-progress stuff.
E) Can someone add a dummy test for a dummy library so that I can see how to run recent gambit with R7RS? Here is an example of such thing: https://github.com/amirouche/arew-scheme/blob/master/src/tests-tests.scm
Gambit has a build-in test framework but I haven't used it yet. We also plan to implement SRFI 64 (A Scheme API for test suites) using the built-in framework.
F) While I am at it, does gambit new module system support introspection or reflection?
I don't know about this one, but it's at least possible to find all the symbols accessible in the current environment: https://misc.lassi.io/2019/gambit-apropos.scm