- 454 instances of "Rc<" in Servo: https://github.com/search?q=repo%3Aservo%2Fservo+Rc%3C&type=...

- 6 instances of "Rc<" in AWS SDK for Rust: https://github.com/search?q=repo%3Arusoto%2Frusoto+Rc%3C&typ...

- 0 instance for "Rc<" in LOC: https://github.com/search?q=repo%3Acgag%2Floc+Rc%3C&type=cod...

(Disclaimer: I don't know what these repos are except Servo).