Project Catalyst is Apple’s official name for what we now as Marzipan. It lets developers port iOS apps to the Mac. I think it can help revive Mac gaming, because presumably games will also be able to get ported. Apple Arcade will be available on macOS as well.
But the big news is clearly Catalyst. Details are still thin, and Apple will most likely share more information this afternoon during its State of the Union WWDC keynote.
Check It Out: WWDC19: Project Catalyst Could Help Revive Mac Gaming