If Servo is a dead end (by the sound of it), what is the new "halo project" that showcases Rust's use in something non-trivial and widely-used/public? (Not trying to rub salt in the wound, geniunly interested.)
Anyway, two big projects in a similar space to QEMU are Firecracker (the underlying virtualization tech for AWS Lambda + Fargate), and Crostini (the underlying virtualization tech for ChromeOS). Firecracker started life as a fork of Crostini and now there's a rich ecosystem going on in this space.
Don't forget the Rust code from Servo that lives in Firefox, too.
Yeah, it's tough to get the combo of all of those things, for other reasons too. I would probably want to first reach for VS: Code, which uses ripgrep for search. But that's a "important component written in Rust", rather than a whole-Rust project. There's tons of tools like ripgrep, which is the most well-known, but it's hard to say how popular they are. And there are things like 1password, which do run on people's machines, but aren't open source.
I actually have recently seen a bug report that implies something really, really huge in this space, but I don't want to jinx it, so I'm not gonna link just yet. We'll see :)
If widely-used doesn't imply open source then there's a lot of options. Dropbox use Rust in their sync client, as well as in their storage backend. Cloudflare are using it for their VPN. Microsoft are rewriting parts of windows in it. Amazon are using it for their Firecracker micro-vms that power lambda.