A Go/weiqi/igo/baduk/goe engine written in Rust. (As should have been obvious from the punny name.)
Math.
Searching for “Go” on crates.io gives roughly a bazillion hits, most of them not about the game. So far, I was able to unearth the following rivals: * joseki (Supports SGF) * libgo (Supports GTP) * baduk (Supports SGF) * go-bag (No features so far)
They mostly seem to be unmaintained, though. (And they have less fun approaches to the necessary calculations.)
One day in the future I might write some useful documentation. Until then, feel free to e-mail me with questions. (Well, after then, too, but not before consulting the docs.)