Remember all the ruckus with various US states introducing operating-system level age verification laws? Colorado and California thankfully exempt open source.
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.
The official Vulkan API Conformant Products list from The Khronos Group recently had Valve's Steam Machine appear on it - so a release is likely quite soon.
Bringing together the worlds of twin-stick arcade shooters with crafting and exploration, Veridian Expanse is another indie game with a demo worth a go.