There are several convenient ways to obtain the Citadel system.
The easiest and quickest way to get Citadel running is to use Easy Install, a one-step installer that automatically downloads, installs, and configures the complete Citadel system on your computer. Easy Install eliminates the need to compile source code manually, and it eliminates package dependency problems.
sudo apt-get install citadel-suite
and follow the questions.
You also can try our debian packages. You'll find i386 and amd64 packages and an apt-source repository there.
Gentoo Ebuilds are avaiable from Sunrise overlay. If you want to give them a try read on here.
Citadel RPM-Packages are available in OBS for all major distributions. Read on here to find out how to install them.
Follow this link to download full source code for the entire Citadel system.