HID Remapper is a useful open-source programmable adapter for USB input devices, with a recent release adding support for Valve's new Steam Controller.
As a bit of a PSA - you might want to ensure you're rather careful with Valve's new Steam Controller charging Puck. Keep anything conductive away from it.
Valve released another new Steam Client Beta update for all platforms on May 13th, bringing with it a few styling changes to Big Picture Mode and various fixes.
The new Steam Controller launched today and thanks to Valve providing GamingOnLinux a review unit, I've been able to put it through some Linux testing.