Varnish is a httpd accelerator/caching server (like squid in reverse
mode), but without the unnecessary disk-thrashing that squid's design
incurs. Target users are system administrators with heavy web stacks -
many vhosts, with content management systems (esp. PHP-based) or java
instances. I have it running on a production machine and there are no
issues to note. Reason for inclusion into factory is to have it all in
one place and not distributed among umpteenth BS repos.