For starters, you can buy a steam gift card with cash. Then buy whatever you like with the card.

But i actually meant it more broadly, you can also use cash for other transactions where you are physically present.

I dislike how much power visa and mastercard have gotten, and cash is probably the best alternative for offline private transactions.

Works for something like PSN. I see cards for sale in local shops. They can presumably be used to claim some funny money in the service that you can pay with.

Steam could probably do the same, but would suck for a smaller operation.

There used to be some cash to BTC machines that would work with any service.