Kill Bill – Open-Source Subscription Billing and Payments Platform
If this supported tons of payment gateways through their plugin system out of the box then it would be worth considering.  But if you go to the page about payment gateways they don't have a listing of 50 integrations you could easily drop in.  Instead they basically say you'll probably have to write the integration yourself:<p><a href="https://docs.killbill.io/latest/userguide_payment.html" rel="nofollow">https://docs.killbill.io/latest/userguide_payment.html</a><p>No thanks - I'll just use a payment processor that has a good API for subscription billing, and a flag on my users table that the subscription is up to date.