- https://github.com/Sylius/Sylius/blob/master/src/Sylius/Component/Payment/Model/Payment.php
- https://github.com/DarvinStudio/DarvinPaymentBundle
- https://github.com/Payum/PayumBundle
- https://github.com/activecollab/payments
- https://github.com/MakingCG/saas-billing
- https://github.com/gvidas/subcription
- https://github.com/ptuchik/billing