The Webbrowser is the bastion, the holy grail of web development and one of the biggest projects in the Rust ecosystem focusses exactly on that. If Rust achieves to run a browser engine, be used to write server code while also being used as the frontend-development language within the browser, then it will truly be the language of the web like no other.
Web Rendering Engine: Servo
Not yet published on crates.io but steady and continuously developed by Mozilla.
Webassembly: Still in design mode
WebAssembly is currently being designed as an open standard by the W3C Community Group that includes representatives from all major browsers. But once it is there, it will only be a question of time until Rust allows to be compiled for that target, too.
Do you know something we don't?
Did we miss an important crate? Or maybe you just recently launched something that should be listed here, too? Let us know!