A worse version of x11rb trying to generate more optimizable code.
The project is licensed under Mpl v2
The project uses a lot of copied and modified code from x11rb, those parts are concentrated at helpers in xcb-rust-connection/helpers, and xcb-rust-protocol/helpers. While that project is an obvious influence on the entirety of those two crates. The license for x11rb can be found at that repo here and included in xcb-rust-connection here as well as in xcb-rust-protocol here.