Zentyal (formerly eBox Platform) is a small business server that offers small and medium businesses an affordable and easy-to-use enterprise-level computer network. It can act as a Gateway, Infrastructure Manager, Unified Threat Manager, Office Server, Unified Communication Server, or a combination of these.
Perlbal is a Perl-based reverse proxy load balancer and Web server. It processes hundreds of millions of requests a day just for LiveJournal, Vox, and TypePad, and dozens of other "Web 2.0" applications. One of the defining things about Perlbal is that almost everything can be configured or reconfigured on the fly without needing to restart the software.