I developed Pysch in order to run SXPath and SXSLT under Python (it works already). I think that Pysch can be used to run any Scheme code.
Any deviations from the R5RS are considered to be bugs. Report a bug.
Tail recursion is supported. Continuations are not supported, but can be implemented if required. Pysch uses the heap-based model as desribed in the “Three Implementation Models for Scheme”[pdf].
Only part of the core standard procedures is implemented. The full list can be found in pysch/func/func.py. If you need a missed procedure, implement it yourself or submit a support request.
Pysch is very slow. I'm not going to fix it yet. I use Pysch for research goals and not in production.
There are several Scheme/Lisp in Python projects. I'm aware of:
The pyscheme page provides more links to other similar projects.
Why don't I use one of the exising projects? See Joel's article “In Defense of Not-Invented-Here Syndrome”.