[KaVir]

Rarely. Far more often the project dies before reaching the point of being playable, and even those muds that do make it usually end up offering nothing they couldn't just have downloaded to start with.

Reinventing the wheel can be fun and satisfying work, but it doesn't ensure a better game. The only thing it guarantees is more work. And depending on your goals, that may be time you could better invest elsewhere in the project.

There are numerous public codebases that meet the requirements of OSI's Open Source Definition, including some in the public domain. Here's a good place to start: