Stripe
I've written a basic stripe checkout handler + a tiny CMS to sell stuff from my site.
It handles basic stock keeping - which was why I couldn't just use Stripe's hosted checkout.
It's not really meant for scale, but it'll handle what I need
just fine - I'm not expecting to be selling a billion thingamajigs
anytime soon!
If you want to purchase the example below for $1, go ahead.
I'll send you a nice email when the payment goes through. Be
warned though, there's only 2 in stock! You really don't
want to miss out! Haha.
Sold out! $2 Profit (minus tax ;_;)
I currently use this on my donations page to accept variable donations as well - so it can handle more than just static product pricing & basic inventory management!