New browser engine from Mozilla. One of its prime objectives is to build an engine that can leverage the multiples cores we have to day and work stuff in parallel. It still not ready for prime use but its growing really well.

IIRC its built with Rust and maybe some unsafe C/C++ code (unsafe in terms of Rust) for things such as the JS engine.

More info about Rust at http://www.rust-lang.org/

More info about Servo at https://github.com/servo/servo#the-servo-parallel-browser-pr...

Wikipedia's explanation is pretty good: http://en.wikipedia.org/wiki/Servo_%28layout_engine%29