As far as playing a virtual piano inside a Half-Life game though, I couldn’t possibly plug anything other than Still Alive.
Half-Life: Alyx is so densely packed with trinkets and goodies to fool around with that it seems it was inevitable folks would cook up some gags with the VR props.
Valve flexed their VR skills in a Tweet the day before Alyx came out.
You can carry two items on the back of Alyx’s gloves, which is mostly useful for carrying health syringes.
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Still Alive (Portal) played on the Half Life Alyx Piano