I would self nominate static-keys, which reimplements Linux kernel static keys for Rust userland applications, and support Linux, macOS, Windows on x86-64, x86 and aarch64.
Static key is a low-level mechanism in Linux kernel, which can speedup usage of seldomly changed features. Due to its complexity and low-level, there are few attempts to bring it to userland. Thanks to the Rust's multi-platform support, great abstraction and low-level operations, we can finally use this great feature in userland applications and on multi platforms.