Mongrel2 - The next-generation Web-Server
The author of Mongrel, Zed Shaw, just released a new web-server - Mongrel2 - which is completely programming-language-agnostic & supports many types of communication protocols besides HTTP (Flash Sockets, WebSockets &c). The nice thing is the simple idea behind it: when receiving a request, it parses it, decides which back-end should handle it & then invokes the back-end via async messaging - using 0MQ - or via sync call - using TCP-IP. This means it can work with back-ends written in any programming-language, & in both synchronous & asynchronous protocols.
The 1st version was released this month. Read here an early announce about it:
& also check out a great interview with its author.