App Stores, the web, etc. How else does software as a service get sold? It’s not a new thing. Probably a lot of these things will just end up as features in existing systems.
Existing appstores like the ones on iOS and Android mostly target casual use cases, mobile devices and on-device software. Not "buy once" experiences for work via software as a service. They also do not offer a unified experience. Two "text-to-speach" apps could have completely different user interfaces.
The web does not have good discovery and reputation management and also does not provide a unified interface. That is why market places like Booking.com, Amazon, Spotify etc have become so big.