I almost hesitate to recommend this because it wants some (lots) more development but I'm kind of in awe of the work done so far in valid. Maybe with some more love and/or a fork it could be great!
waitlist - A queue of std::task::Wakers that can be woken in order, or all at once. Useful for building synchronization structures between tasks in async rust (mutexes, condition variables, channels, etc).
I would like to self-nominate wundergraph here. It provides a static graphql API based on a relational database. It's build on top of diesel and juniper.
plotly for rust - Although it may seem like self-promoting I have to say having a plotting library that's on par with what's available in Python has allowed me to reach for Rust more often.
I'll nominate process_control. It makes it easy to terminate a process after a timeout, which is surprisingly difficult to do correctly. Different platforms have different types of identifiers, and some may be recycled for other processes.
stork Impossibly fast web search, made for static sites.
A strange one to recommend because it isn't actually on crates.io (a different crate called stork is). I think it is a very cool use of rust to make a combined binary tool and wasm js library