The Test Case DataBase project has had a boring history, including much neglect. The original version's authors aren't even testing anymore. This project has been revived to fill a need of replacing an expensive commercial product that fails to live up to its purpose.
Focus: The focus of the tcdb is to make it easier for testers to do their job. Test leads and testers shouldn't have to be at odds with their organization tool, just so that their manager can get reports. All organization and workflow allow ease of use for the tester.
The difference: Other open and closed source test case databases are focused on a manager's point of view, because that's who you sell it too. They also seem to completely forget that a tester has to basically "live" inside a tcdb, and to make it as enjoyable as possible. Basically we want to build a tcdb that you don't think "I could do this sooo much better" or "Why are they making me use this?" the whole time you're using it. We want to make the tester happy, while not annoying everyone else that has to use the system.
Who are we: Testers. We are the ones doing the job. We write test cases, automation, and run them. We also have some development skills, which helped us realize why these other tools were just a joke.