Kagi was one of the earliest, especially on the Mac. But there were others like SWREG, ShareIt, eSellerate, Plimus, Cleverbridge and many others. The Black Cat Systems Overview Of Shareware Registration Services [1] used to be the chart you'd send newbies to when they asked which e-commerce service to use.
Whenever a new service started up, it would almost always get acquired by Digital River (aka "The Borg", since they assimilated everything and resistance was futile).
Some of those services are still around, like FastSpring and Paddle. Avangate ended up buying 2Checkout and then rebranding to call themselves 2Checkout. The main advantage of those companies now is they offer global tax compliance, now that the EU and several other countries want you to charge and collect tax based on where the customer is, not where your business is.
Stripe pretty much came along and crapped on all of that ( in a good way ). And lowered the barrier to entry so indie dev shops could accept CC payments seamlessly as the other big megacorps.
Stripe is not a thing in most of the countries on this planet.
