RunVCS is a restricted shell which allows the user to run version control software and only access specified repos. It also provides other useful features such as changing the username which is passed to programs. Only SVN is supported currently, but more VCS will be supported over time.
If you find a bug, have a suggestion, etc, please email me.
The RunVCS SVN repository can be checked out from the following URL:
http://www.solemnwarning.net/svn/runvcs/trunk/