HitPay - Send or receive money using a modern payments interface

Mailman - Mailman is free software for managing electronic mail discussion and e-newsletter lists.

Unlock - Monetize your content with a few lines of code

Mailman 3 - Dedicated Mailman 3 installation. Unlimited lists/configuration. Free subdomain at mailman3.com. Dedicated support for list admins.

Stripe - Online payment processing for internet businesses. Stripe is a suite of payment APIs that powers commerce for online businesses of all sizes. Use Stripe’s payment platform to accept and process payments online for easy-to-use commerce solutions.

MailChimp - MailChimp is the best way to design, send, and share email newsletters.