H2O (web server)

is a free and open-source web server. It is written in C, and is distributed under the terms of the MIT License.
It was designed with a focus on supporting HTTP/2 and TLS, maximizing the use of new web technologies such as prioritization and server push. As a result it achieves significantly better performance than conventional web servers such as nginx.

Features

has the following key features:

HTTP/1.0 and HTTP/1.1 support
HTTP/2 support
* Full support for dependency and weight-based prioritization with server-side tweaks
* Cache-aware server push
HTTP/3 support
TCP Fast Open
TLS support
* Session resumption
* Session tickets with automatic key rollover
* Automatic OCSP stapling
* Forward secrecy and fast AEAD cipher suite
* Private key protection using privilege separation
* Encrypted Client Hello
Static file serving
FastCGI support
Reverse proxy
Scripting using mruby
Graceful restart and self-upgrade

In, started development of for usage as a server for mobile games while working at DeNA. The initial version was released in, and the first stable version was released in when the HTTP/2 specification was finalized.