A quine is a program that takes no input, and it's output is it's own source code. A quine-relay is a program that outputs the source code for another program, and when that next program is run it outputs the source code of the first program. I recently saw this quine relay program which was super impressive as it goes through 128 languages like this!
Having recently learned some Rust, I thought I'd write a simple quine in rust. It wasn't actually as difficult as I imagined, this took about 25 minutes. The rust standard library has a really convenient function escape_default which made it pretty easy!