Memberstack is a JavaScript library for front-end designers and developers who want an easy way to set up user authentication, gated content, and secure payments for their membership site. Definitely not for beginners or folks without strong web design and/or dev skills.

API info:

Front-end API

Works well with Webflow:

Webflow Memberships | Memberstack

Payments are currently just through Stripe:

Supported payment gateways

Affiliate set up is available via Rewardful:

Rewardful

Main differences between Basic and Professional are:

• Basic is capped at 1,000 total members; Professional allows up to 10,000 total members
• Basic charges a 4% transaction fee; Professional charges a 2% transaction fee