Mixom

Mixom Tools (or simply Mixom) is a company in later ID Software Doom games, such as Doom 3, and the reboot.

Doom 3
Shown as a supplier of several different technical tools, devices, and office furniture. During the story, Mixom mistakenly ships a number of chainsaws to the UAC base on Mars, in place of the requested jackhammers.

Looking closely in some cutscenes the player may be able to see the Mixom logo on the side of telephones around the UAC base. It also occurs on doors, some computer terminals, Portal pads and other devices. Upon Marine's First arrival in Hell, The broken portal pad can visibly read "Mixom". Additionally, a newsreel plays on a TV early in the game (before all hell breaks loose) about Mixom and its rival company comically named, Moxim suing one another for various reasons.

Doom (2016)
Mixom returns in the 2016 reboot of Doom, they are the manufacturers of the various doors on the UAC site. It's possible to also find it's rival, Moxim's doors, and products as well.

Trivia

 * Mixom Tools is most likely a Japanese based company, as the Doomguy eventually finds an e-mail which refers to a Mixom website, Mixom.co.jp (the link is dead in the real world). .jp is an Internet country code top-level domain for Japan.
 * In Rage, Mixom is featured as a remnant of the old world, operating a chain of gas stations among other things. It is one of several hints within the game that seem to indicate it occurs inside the same universe as Doom 3.