I was just looking at Tiki which recommended esehttpd in the documentation.

I've never heard about it before, but apparently it is a very fast web
server with Ruby intergrated into its core - how cool is that :-)

The site is in japanese, but there is english documentation in the download.

http://ghost.math.sci.hokudai.ac.jp/esehttpd/sources/

It only works for Linux (at least only tested on Linux), and achieves
additional speed with realtime Posix extensions available in 2.4.x kernel.

Mikkel