What operating systems are supported?

Citadel is intended to run on any Unix-like operating system. The primary development platform is Linux, running on 32-bit Intel. It is also known to work on Solaris (version 8 or newer), FreeBSD (version 6.0 or newer), OpenBSD (version 4.0 or newer), and Mac OS X (version 10.1 or newer).

If your question is actually “I want to build a Citadel server, what operating system should I use?” then you would probably be best served by running Linux.