The article attributes all these free engines to Unity but I think they've missed 20+ years of videogame history.<p>First, Valve has always been very open to game mods. Some of their most popular franchises (TF & CS) grew out of the mod community around HL1 and they've always made tooling available for the Source engine.<p>HL1 was based on the Quake engine and id has always embraced the mod community. Id software has also contributed greatly by open sourcing their old engines.<p>The Torque Game Engine (Tribes) was opened up to low cost licensing by GarageGames in the early 2000s.<p>Unreal has long made their tools available for free, though licensing wasn't quite favorable to the indie developer until more recently.<p>Blender made an attempt at including a game engine but it never really took off from my point of view, although they're still including and improving it.<p>Even Blizzard's inclusion of map tools with Warcraft 3 spawned one of the biggest gaming trends of the past 10 years, DOTA / MOBA games. Though these have all been recreated with other engines (including Valve's Source), the inclusion of modding tools with games is part of the story and some of the competition that the current crop of free tools must face.<p>Open source deserves a mention as well. Ogre 3D, the above mentioned Blender, and other engines and especially tools have sprung up in a variety of games and often fill missing gaps in asset creation.<p>Unity certainly deserves some credit, however. Their simple tooling, relatively early start on mobile, and aggressively lowering the barriers from side project to published game has definitely moved the goalposts for game tooling. The Unity Asset Store is also a great thing.<p>I've really only scratched the surface though. XBox DNLA deserves a mention, the role of the iPhone and mobile in general has been huge, Minecraft's until recently ambiguous quasi-open source nature, and there's many more. We're in a golden age of game creation and I hope to play some amazing new game ideas. I realize there's also going to be an abundance of mediocre imitations from creators like me but its all part of the fun.