This is a pure-ruby port of Takuma Ozawa's RBTree. (it has an identical interface and uses the identical unit tests from his version 0.3.0, however it is *not* a Red-Black tree.) It's intended for doing lookups and not for doing lots of insertions or deletions. Please see RBTree docs for a sense of how this is supposed to be used. (This one runs the unit tests about 15% slower than Ozawa's C-version, and 80% less lines of code ;)