It seems every PC maker is suddenly on a quest to build smaller sized gaming rigs, presumably because they envision these boxes taking residence in your living room where they'll host Steam games on your big screen TV. One of the newer candidates is CyberPowerPC's Hadron Air, a mini iTX based gaming system that measures all of 6.6 inches (W) by 12 inches (H) by 12.1 inches (D).
To be clear, CyberPowerPC isn't marketing this as a Steam Machine, though there's nothing stopping you from fragging in your living room. Regardless of where you put it, you have two base systems to choose from in the lower end tier, both of which are fairly tame in configuration (more on that in a moment).
The first is the Hadron 100a ($599). It includes an EVGA Hadron Air case with 500W 80 Plus Gold Certified power supply, AMD A6-6400K processor (3.9GHz) with Radeon HD 8670D graphics, AMD A75 chipset motherboard, 4GB of DDR3-1600 RAM, 500GB hard drive (7200 RPM), 24X slot-loading DVD burner, and Windows 8.1 64-bit.
Prefer Intel? The Hardron 100i ($799) features the same case, optical drive and OS, but comes with an Intel Core i5 4440 processor (3.1GHz), Intel Z87 Express Chipset motherboard, Intel HD graphics, 8GB DDR3-1600 RAM, and 1TB hard drive (7200 RPM).
Both are respectable, though if you have additional funds to toss at either configuration, you can customize your build with faster processor options, SSDs, and even full size graphics cards like the Radeon R9 290X or GeForce GTX Titan. There are also higher end baseline systems to choose from, including the Hadron Air 200i (starting at $1,135) and 300i (starting at $1,589).