What are some less popular but well-made crates you'd like others to know about?

Title. I've kinda been going around making a nice big bookmark list of potentially useful Rust libraries, and I wanna ask y'all, what are some well-made yet less popular libraries that you think people should know about? Like, stuff that isn't exactly at the top of lib.rs/crates.io, but feels like it's the quality of many of the crates that are at the top?

Here's some of mine:

• opaque-ke: Well, it's less the crate itself, more the thing it implements, but OPAQUE is a really cool password encryption/key-exchange thingy, where not even the server knows your password at any point whatsoever. I kinda wanna work on something so I have a chance to use it.
• multiversion: This crate allows you to automatically make multiple 'versions' of a function for different CPU features. For example, if a function benefits from auto-vectorization, you could use this crate to make x86_64+avx and aarch64+neon versions of a function, and the crate will handle stuff like automatically selecting which version of the function during runtime.
• extrasafe: This is a Linux-specific crate, which allows you to "limit" your crate from doing certain syscalls. For example, if your program is never going to connect to the network, you could use this to ensure your program is incapable of connecting to the network, as a kind of exploit protection system.

I wanna know what useful crates y'all know about!