Ultima Online: 4 Open Source Clones Compared
OUO is structurally different from the other clients listed here: it's a reverse-engineered reimplementation of the Ultima Online server itself, built from data extracted from the free 1998 Ultima Online Demo, rather than a client connecting to someone else's server. Iris2, separately, doesn't reuse Ultima Online's original art — its models and textures were created by its own small team, without a formal license currently attached — even though it still needs a legally patched UO installation to connect to and play.
Comparison table
Availability
- Status
- Playable
- Platforms
- Linux, Windows, Web, OSX
- Play in browser
- YesPlay in Browser
- Mobile
- No
Project health
- Development status
- Active
- Last updated
- 7d ago
- Stars
- 723
- Contributors
- 95
- License
- BSD-2-Clause
- Engine
- —
Compatibility
- Requires original assets
- YesRequires legally obtaining a copy of the Ultima Online Classic Client; the project does not distribute any copyrighted game assets.
- Multiplayer
- Online
Availability
- Status
- Playable
- Platforms
- Linux, Windows, OSX
- Play in browser
- No
- Mobile
- No
Project health
- Development status
- Active
- Last updated
- 7d ago
- Stars
- 177
- Contributors
- 27
- License
- AGPL-3.0
- Engine
- —
Compatibility
- Requires original assets
- YesThis is a client for Ultima Online; you need an Ultima Online server to connect to.
- Multiplayer
- —
Availability
- Status
- Semi-playable
- Platforms
- Windows
- Play in browser
- YesPlay in Browser
- Mobile
- No
Project health
- Development status
- Active
- Last updated
- 12d ago
- Stars
- 159
- Contributors
- 4
- License
- —
- Engine
- —
Compatibility
- Requires original assets
- NoServer data from UoDemo is included and can be used; no original commercial Ultima Online assets are required to run.
- Multiplayer
- Multiplayer
Availability
- Status
- Playable
- Platforms
- Windows, Linux, OSX
- Play in browser
- No
- Mobile
- No
Project health
- Development status
- Halted
- Last updated
- 4y ago
- Stars
- 25
- Contributors
- 1
- License
- —
- Engine
- Ogre3D
Compatibility
- Requires original assets
- YesRequires a legal copy of Ultima Online, patched to version Age of Shadows or later (Samurai Empire, Mondain's Legacy, or newer).
- Multiplayer
- Online
| Title | ClassicUO | CrossUO: Ultima Online | OUO | Iris2 |
|---|---|---|---|---|
| Status | Playable | Playable | Semi-playable | Playable |
| Platforms | Linux, Windows, Web, OSX | Linux, Windows, OSX | Windows | Windows, Linux, OSX |
| Play in browser | YesPlay in Browser | No | YesPlay in Browser | No |
| Mobile | No | No | No | No |
| Project health | ||||
| Development status | Active | Active | Active | Halted |
| Last updated | 7d ago | 7d ago | 12d ago | 4y ago |
| Stars | 723 | 177 | 159 | 25 |
| Contributors | 95 | 27 | 4 | 1 |
| License | BSD-2-Clause | AGPL-3.0 | — | — |
| Engine | — | — | — | Ogre3D |
| Compatibility | ||||
| Requires original assets | YesRequires legally obtaining a copy of the Ultima Online Classic Client; the project does not distribute any copyrighted game assets. | YesThis is a client for Ultima Online; you need an Ultima Online server to connect to. | NoServer data from UoDemo is included and can be used; no original commercial Ultima Online assets are required to run. | YesRequires a legal copy of Ultima Online, patched to version Age of Shadows or later (Samurai Empire, Mondain's Legacy, or newer). |
| Multiplayer | Online | — | Multiplayer | Online |
| Preview | | | |
Known limitations
- compatibility: Tested mainly on Linux; other POSIX operating systems should be supported but are not fully verified.
Frequently asked questions
Are the Ultima Online clones on this page open source?
Yes — every clone catalogued here is an open-source project. Availability, license, and development-status details for each one are listed in the comparison table above.
What license do these Ultima Online clones use?
ClassicUO (BSD-2-Clause); CrossUO: Ultima Online (AGPL-3.0).
Do I need to own the original Ultima Online to play these clones?
OUO runs standalone, no original files needed; ClassicUO, CrossUO: Ultima Online, and Iris2 require original game assets to play.
Can I play any of these Ultima Online clones directly in a browser?
Yes — ClassicUO and OUO have a browser-playable build linked in the comparison table above, no install required.
Which Ultima Online clone is the most actively maintained?
ClassicUO, CrossUO: Ultima Online, and OUO are currently under active development, based on recent commit activity. See the "Development status" row above for every clone's current status.
See the full write-up for each clone, or go back to Ultima Online.