Varnish is
* a high-performace HTTP accelerator designed for content-heavy
dynamic web sites.
* designed for maximum performance on modern hardware and modern
operating systems. Varnish takes full advantage of modern virtual
memory systems and of advanced operating system features such as
kqueue, accept filters, sendfile etc. where available.
* open source, published under a two-clause BSD license.
From the website:
Varnish is very, very fast - ten to twenty times faster than
Squid on the same hardware.
http://www.varnish-cache.org/
