Sphereserver  
   Official home of the sphere software and client.
   http://www.sphereserver.com/

RunUO  
   A Microsoft.NET server, with the goal of being easy to use.
   http://www.runuo.com/

Ultima Offline Experiment  
   Resource and news information page for UOX3.
   http://www.uox3.org/

Wolfpack  
   Wolfpack is a free Ultima Online Server Software, easy to use and script.
   http://www.wpdev.org/

UO RICE  
   An encryption removal tool, required for logging in to most emulators.
   http://stud4.tuwien.ac.at/~e9425109/UO_RICE.htm

Ryandor's UO Map Making Site  
   Specializing in information and tools for creating custom maps.
   http://www.ryandor.com

ADMIX-X-NetWork  
   Online game news and resources
   http://ax-n.net

SteamEngine  
   Open-source C# UO server software package. Easy to use, yet still very powerful.
   http://steamengine.sourceforge.net

Nox Wizard  
   A highly scriptable open-source server emulator, capable of running on various platforms.
   http://noxwizard.sourceforge.net/

The Box  
   Home of Pandora's Box, a popular GM tool for RunUO. Also offers some other RunUO utilities.
   http://arya.runuo.com/