MemberPress – The best, full-featured Membership platform plugin for WordPress. Protect all or some of your content with simple Rules, and charge members for access to that content. Integrates with many other services like Stripe, PayPal, MailChimp, ConvertKit and many others.

Members – A free, but easy to use Roles and Capabilities editor for WordPress Users. Includes some very basic Content Restriction features also, however MemberPress is much better in that capacity.