Uodemo.exe
From UODemo Wiki
This is the Win32 executable for the Ultima Online Gold Demo. It comes with an installer on the Ultima Online Gold CD, the demo requires that the client is installed becauses it uses the graphics and sounds from the client installation.
The version on the CD is 1.09. If there are other version of uodemo.exe out there, we would like to know.
It's been proven that the uodemo contains a full server and a full client. The client and server communicate with each other with the same protocol as the regular client and official OSI servers did back in the days. Unlike the official protocol the packets are send unencrypted. Also note that these packets are not send through sockets but by the simple means of a linked list in memory.