New SMART Plugins project for WordPress is Smart bbPress nVerify. This plugin is made for authors selling through Envato Marketplaces allowing them to setup customers purchase code validation for support forums powered by WordPress/bbPress.
Plugin hooks into bbPress templates loader so it can replace normal templates with restricted access templates. Purchase codes are stored with user accounts for auto verification on future visits. Plugin can also revalidate codes after set period of time, and you can add more than one product to individual forums.