NOTE: You may have to run the WurmLauncher.exe as administrator. Navigate to your WurmLauncher.exe file, right click it, Properties, Compatibility, check the box for Run this program as an Administrator, Ok.

VIDEO: Freth's video on how to run an alt with Wurm Unlimited

1. Navigate to your Wurm Unlimited folder. If you're unsure where the game folder is you can navigate to it through Steam by right clicking on the library listing, Manage, Browse Local Files.
2. Go to your WurmServerLauncher folder.
3. Copy the file named steam_appid.txt to your WurmLauncher folder.
   

Read the paragraph below.

You can now run more than one copy of Wurm, but you must run subsequent copies of the launcher from outside of Steam. The best way I've found is to right click on the already running Wurm Client icon on the taskbar and run another instance of Wurm Client. I keep my Wurm Client pinned to my taskbar, so that it is always there and just load it from that icon for both the primary and alt instances.

1. Follow the Windows steps above taking into account that Linux will have a different path. Again, you can use Steam to find your folder as per step 1 above.
2. Move the libsteam_api.so found in the WurmLauncher folder to the nativelibs folder.
3. Run the executable, which is “WurmLauncher” (no extension) outside of Steam.