There are 2 file types use the .MUL file extension:
1. Ultima Online Multi File
Game file used by Ultima Online, one of the earlier massively multiplayer online (MMO) games; may save various kinds of data, including graphics, animation data, maps, and game items; also used for applying game patch updates.
Sometimes Ultima Online users modify the contents of MUL files to alter gameplay. Tools such as MULTtool, Multibuilder, and MulPatcher can be used. However, since Ultima Online is an older game, some of these programs may be difficult to run on recent operating systems.
Updated: October 19, 2020
2. Deus Ex: HR Multiplexed Audio File
Audio file used by Deux Ex: Human Revolution (DXHR), a first person role-playing game; saves audio data in a native format used by the game; can be demuxed to the FMOD .FSB format using Gibbed's Deus Ex HR tools.
Updated: July 13, 2012