E.g. I have written a cache-warmer that preopens and does readaheads (posix_fadvise) for assets from NFS and offers the already open file descriptors to the calling process. The NFS share offers decent throughput but terrible latency (compared to NVMe). Opening files is slow, walking directories sequentially is slow. And then hitting cold pages is slow. Doing all this in rust and handing the file descriptors over to node lets me reduce minutes to seconds. But if someone doesn't like it, there's a flag that turns it all off, back to the slow path.
Another use is essentially replacing shell-scripting when some REST APIs, JSON parsing and so on are involved. E.g. to glue together some status reporting in CI. There are so many different unreliable APIs without client libs involved that I appreciate the error handling.
I use it for all my personal projects as well. Which are basically the same types of things I wrote in Go. Though, I also am experimenting with WASM DOM UIs, something I've not yet used in Go.
People are using rust as they do other general purpose programming languages that have somewhat of a focus on systems programming: to write code. Your question isn't really easy to answer in the same way that someone asking "what are people building with python?" isn't useful. The answer is everything from webpages to text editors to operating systems, and everything in between.
I have a feeling that inside of 5 years Rust will be blowing up on the job market. It's just so good and so practical that once you pick it up, anything less well designed will feel like a kludge and hack that might blow up on you at any point.
My current pet project in Rust is writing a functional language compiler that compiles down to System F/F omega and eventually I'm going to build some kind of virtual machine
I also have a lot of personal pet projects written in rust: an MMORPG-style game, accounting software, various WASM widgets, some OS fiddling, some work extending servo as a browser that implements umatrix-like control but lets you set options per domain (e.g. 3rd party cookie, user agent setting, etc, all per-domain).
I've also contributed a number of small libraries that I wrote for my projects to open source (textnonce, float-cmp, mailstrom, formdata, mime-multipart, solvent, ddsfile, pemmican, resolv-rs, email-format, and others).