Greene, who was from VMware by its owner EMC last year, is one of several investors putting $5.5 million into , which makes a game platform for the Nintendo Wii, iPhone, PCs, Macs and Web browsers.

The company's Series A investment round was led by Sequoia Capital and also included Greene and Atari CEO David Gardner. Greene and Sequoia partner Roelof Botha are joining Unity's board of directors.

Unity makes a software development package with a 3D game engine.

"The Unity platform is currently used in world class games such as Tiger Woods PGA Tour Online by Electronic Arts, the Quest for R2D2 by Lego and FusionFall by Cartoon Networks," the company says. "Earlier this year, Unity for iPhone was released and to date, more than 325 games are using the Unity engine to power their iPhone games, including Zombieville USA, one of the top 10 iPhone games measured by units sold."

Unity's Web site shows a humorous side to the company, with statements such as "Fact: Unity is made of flying ninjas" and "All your phones are belong to us." Unity's CEO and co-founder is David Helgason, who previously worked with news and community integration, music distribution and consulting start-ups.