Maybe you are thinking of Monotone. It shares some design, such as referencing commits by their hashes and zero copy branching. I think Linus said at some poin

Maybe you are thinking of Monotone. It shares some design, such as referencing commits by their hashes and zero copy branching. I think Linus said at some point that if only performance would have been sufficient for the Linux kernel, there would have been no git (but don't quote me on that).