There are some stuff where open source reimplementations would be good to have. The things you mention seems like good to have a open source reimplementation of

There are some stuff where open source reimplementations would be good to have. The things you mention seems like good to have a open source reimplementation of, but I do not know of the specific projects. Another thing is game engines, such as ZZT (by Potomac Computer Systems) and Hero Mesh (by Everett Kaser Software). I have figured out many things about their working, but I may have missed some details. I have the wiki for making Free Hero Mesh with some of these details that I know of, but may have missed some. But the question is also valid of which software you are interested in, too.