RoadRunner is an open source (MIT licensed), high-performance PHP application server, load balancer and process manager. It supports running as a service with the ability to extend its functionality on a per-project basis.
RoadRunner is written in Go, and can be used to replace the class Nginx+FPM setup, boasting "much greater performance". I'd love to see some benchmarks. Better yet, I'd love to see someone use this in production for a bit and write up their experience.