Varnish Cache (VC) is a powerful open source HTTP engine/reverse HTTP proxy that can speed up a website by up to 1000 percent by doing exactly what its name implies: caching (or storing) a copy of a webpage the first time a user visits.
Make your websites fly - Varnish Cache (VC) performs really, really well. It is usually bound by the speed of the network, effectively turning performance into a non-issue. We've seen Varnish delivering 20 Gbps on regular off-the-shelf hardware.
Flexibility and freedom - Full flexibility with Varnish Configuration Language (VCL) - Make your own rules!
Open Source - Varnish is free software licensed under a two-clause BSD licence, also known as the FreeBSD licence. The project was initiated in 2005. Varnish Cache 1.0 was released in september 2006.
Varnish Cache 5 (VC) (Ubuntu)
Help is provided through community documentations, IRC channels and forums