GMS is a contact relationship management system initially written for the one-person consulting shop, although it can be used for teams as well. A multi-user version will be released in the future.
GMS contains the standard contact management features you would expect, plus the ability to create and track "Items" that can both be displayed on calendars and be invoiced later. Default Items include Block Hours, Phone Calls, Hours, Scheduled, Expenses, Notes, products for sale. Simple invoicing is included but may not replace a real accounting package (it does work for me, though.)
UPDATE Oct 19, 2009: The version here has some bugs and incomplete features. In the meantime I have done a lot more work on it, including integrating a lot of Getting Things Done (GTD) principles. On the other hand, I haven't seen a lot of activity here so I haven't bothered to update anything here. But I will if people are interested.
The application is just 1 database but can optionally be integrated with your e-mail with the addition of 2 simple views to your mail file, allowing easy access to electronic communication with all your contacts.