Arguably, one of the best things about Valve's Steam Controller is its software component -- an interface that allows user to assign any button of their controller to a myriad of keyboard functions. Its a feature that lets gamers make any PC game playable by controller -- even if it was only designed to be used with a mouse and keyboard. The interface is so good, Valve enabled it for PlayStation 4 controllers earlier this year. Now they're enabling it for pretty much everything else: the latest version of Steam's beta channel will let you fully customize the Xbox 360 gamepad, the Xbox One controller and any other input device that uses the Xinput standard.
It's a good update, but there's a reason it's still on the beta channel. Right now, there's no way for Steam to differentiate between different kinds of Xinput controllers -- the configuration interface can't tell the difference between an Xbox One gamepad, a 360 controller or a generic Xinput device. This makes it hard to save controller specific profiles, and means some gamepads with fewer buttons won't be compatible with community gamepad profiles.
Still, it's a good step forward in compatibility for PC gamers. Once the bugs are worked out, you'll be able to play almost any PC game with almost any game controller.