The HyperText Transfer Procotol, or the reason you're looking at this page right now.
(todo: insert relevant RFCs, especially the WebDAV ones)
- thttpd - can be compiled with PHP
- Nanoweb - PHP as its own web server
...and a cast of thousands.
- Pylot, a load testing tool with nice reporting output.
- tinyproxy - I once modified this to build a content adaptation proxy for mobile devices, back when such things were necessary. Highly recommended.