In addition to nathan7's answer, there's also terminal.com (and I'm assuming here that we're not counting Mozilla's usage of Rust in Servo (and soon Firefox)). There are other companies putting various pieces of Rust code through their paces and we have outreach programs to help these companies in their explorations (I don't like name-dropping before announcements are fully ready, I'll be able to say more later this year).

In general though, remember what a young language Rust is (May wasn't that long ago!) and understand that large and notable projects take time to appear. Docker didn't appear until Go 1.0 was one year old, for example.

MaidSafe (http://maidsafe.net) and Skylight (https://skylight.io) are both written in Rust, Maidsafe having recently moved to it from C++.