WooCommerce

Buy a product, gain a membership. WooCommerce purchases apply tags that grant or revoke access automatically.

WooCommerce is the checkout most WordPress sites already have, and the usual way to sell a membership through it is ugly: buy the product, then someone or some plugin manually creates the member, then the CRM catches up by email. Every step is another place for the order to arrive half-processed.

The integration closes the loop. A WooCommerce order applies tags the moment the order completes, so the purchase is the delivery mechanism. Buy the "Gold Membership" product and the gold tag lands on your member record in the same breath. Refund the order and the tag comes off, closing access without a support ticket.

The store also gains membership awareness in the other direction. Shortcodes can check what is in the current member's cart, whether they have purchased a specific product, or whether the cart is empty, so you can show upsells to members who haven't bought yet and skip the pitch for those who have. Products can be added to the cart directly from a page with a shortcode, which turns any landing page into a one-click checkout.

For access control rather than commerce, the same rules apply: content can be gated on cart contents or purchase history, not just tags, when that is the more natural condition.