PyLETS

PyLETS is written in Python and is known to run on Unix and Linux.
It is a web-based CGI programme, and it uses file locking for data persistence so is very low cost, not needing a relational database backend. Nightly backups to another site are handled by email or rsync. In practice it will run on any platform that can do Python CGIs including Windows. Minimum system requirements are whatever will run your web-server, eg Apache - please refer to web server documentation.

PyLETS was first written in 2002 and has been updated continually since then. No support is offered formally, though assistance is likely to be available on request to support installation for the next 10 sites to adopt it after March 2009. The current version is 0.9, released Aug 2008, which includes support for wants and offers as well as accounts. It is being used by Coventry LETS, where Richard Kay the PyLETS developer is the LETS database maintainer.
Feedback so far is that "it works much better than the paper-based system it replaces".