http://www.haproxy.org/
Things to follow up on:
(1) How is zero copy done? Using the "splice" system call on Linux
(2) MRU memory allocator
(3) Accepting multiple accepts at the same time across different processing listening to different ports of course.
(4) Tree based storage e.g.making heavy use of the Elastic Binary Tree http://wtarreau.blogspot.com/2011/12/elastic-binary-trees-ebtree.html