Imba is a programming language for building web applications with insane performance. You can use it both for the server and client.

Use Open Swoole to build high-performance, scalable, concurrent TCP, UDP, Unix Socket, HTTP, WebSocket services with PHP without too much knowledge about non-blocking I/O programming and low-level Linux kernel with fiber and coroutines.

RoadRunner is a high-performance PHP application server, load-balancer, and process manager written in Golang.