We should probably note right off the bat that a “green gaming PC” is a sort of contradiction in terms, akin to the world’s “smallest giant panda.” But that doesn’t mean Maingear’s aim with the Pulse is completely bonkers: essentially it’s a low-power machine that still aims to provide a good gaming experience. Short of going the nettop route and note quite going ridiculously green, there’s a middle ground where you’re using advanced but low-power components, creating something that won’t dim your lights when you turn it on, yet can play Call of Duty 4.
The specs are modest: A low-end 45nm Core 2 Duo or Quad and a GeForce 9800 GT ECO running on an ION chipset, altogether drawing about 165W. You’ve got plenty of room for RAM (up to 8GB), and a regular hard drive (if you want greener, you can go with SSD). It’s got 7.1 audio and a nice shorty-tower case, plus it doesn’t break the bank, starting at $799.
I’d go further and get some passive cooling in there — with no spinning drives and no fans it’d be quiet as a mouse as well as a power saver.