The only real competitor to the Mac App Store in terms of a games provider is Steam, which is arguably the main source of material for Mac gamers. However The Verge reports that the Steam could be going even further to compete with Apple, as its official Android app leaked categories that aren’t gaming related, including audio production and software training.
Whether this is something that is indeed coming to the Mac remains unclear, but when checked the categories were empty. They were removed shortly afterwards, confirming that it was a leak.
It isn’t unreasonable to assume that Valve will want to try and compete with Apple in terms of app sales though, and with its already very high user base, you’d imagine that many would be interested in buying apps via Steam alongside their games.
However all this is completely speculation, and it could be nothing at all. Nevertheless, it would make perfect sense, so we’ll have to wait and see.