“Varnish is a state-of-the-art, high-performance HTTP accelerator.” (varnish-cache.org). It’s configuration language VCL makes it very flexible – it even allows to use custom inline C code 
In the past I always build varnish from source myself and used checkinstall to create deb packages. A few days ago I came across a post by Trevor that simplifies the installation on Debian/Ubuntu:
- make sure you have all requires libs/tools installed:
apt-get update apt-get install subversion autotools-dev automake1.9 libtool autoconf libncurses-dev xsltproc quilt
- checkout the varnish source code from svn (change version number as needed)
svn co http://varnish-cache.org/svn/tags/varnish-2.0.6/
- build deb packages
cd varnish-2.0.6/varnish-cache/ dpkg-buildpackage
- install (package names may differ depending on the architecture, e.g. i386 instead of amd64)
cd .. dpkg -i libvarnish1_2.0.4-6_amd64.deb dpkg -i varnish_2.0.4-6_amd64.deb
- you can now change the config in /etc/varnish/default.vcl and /etc/default/varnish