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

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

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

UOX Classic
- Home of the classic branch of UOX, without the Javascript engine.
- http://www.uoxc.com/

LoneWolf Emu
- A free open source server emulator intended to provide solid baseline code for others to base their own development on.
- http://home.tiscalinet.de/aduke/main2/news2.htm

SphereServer
- Official home of the sphere software and client.
- http://www.sphereserver.net/forums/

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

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

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

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

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