About
Ultima Online is a fantasy massively multiplayer online role-playing game released on September 24, 1997, by Origin Systems. Iris2 is a third-party 2D/3D client for Ultima Online, built on the Ogre3D engine by a small team (Florian Fischer, Robert Noll, and Sebastian Dorda). It requires a legal, patched copy of Ultima Online with one of several supported expansions (Age of Shadows, Samurai Empire/Gold Trial, or Mondain's Legacy or later) to connect to and play, and runs on Windows and Linux. Development appears to have halted.
How it differs from the original
Iris2 doesn't reuse Ultima Online's original assets — its models and textures were created by the Iris team specifically for the project without a formal license currently attached, and the team notes they were in the process of replacing them with new Creative Commons-licensed art.
Getting started
It requires an existing, patched Ultima Online installation with a supported expansion; after installing Iris2 itself (which also installs the needed Visual C++ runtime and DirectX 9), running its updater completes setup before play.