[MisterTea]

id sold a few Doom and a bunch of Quake 1/2/3 licenses back in the day. Off the top of my head: Heretic and Hexen used the Doom engine, their sequels used the Quake and Quake 2 engines respectively. Strife was an FPS RPG that was Doom based. Half-Life started out as a HEAVILY modified Quake engine and rumor has it that there is still a bit of Quake code in Source. Duke Nukem Forever started out on Quake before moving to Unreal.

[partiallypro]

Call of Duty and Medal of Honor both used id Tech 3 (aka the Quake 3 engine), as did some of the Star Wars games, etc. Unfortunately, The Source Engine came out around the time of id Tech 4, and it really took the reins, with Unreal Engine hitting a stride thereafter. https://en.wikipedia.org/wiki/Id_Tech_3#Games_using_a_propri...

[rasz]

I heard an interview about Doom port to hmm 3DO? and it cost them one time payment of $50K cash money to outright buy Doom assets + game engine license.