You can login to the bugtracker at webempoweredchurch.org. If you don't have an account yet you can get one here.
For feature requests please choose 'feature' in the severity dropdown.
Please contact Jeff Segars (jsegars(at)alumni.rice.edu) if you want to write, update or translate the cal documentation.
You can use paypal to donate. Please contact Mario Matzulla (mario(at)matzullas.de) if you want to donate. Mario can write an invoice for the donated amount.
If you're into PHP and TypoScript you can help the calendar developers to develop new features. All Developers work on a shared code base in our SVN-repository.
http://svn.webempoweredchurch.org/repos/calendar
(requires a client like TortoiseSVN or PHPeclipse/subclipse)
Please contact Mario Matzulla (mario(at)matzullas.de) before uploading/commiting any changes!