Elite Licenser is a WordPress plugin for any types of product licensing. It also manages product updates, auto generates license code, built in Envato licensing verification system, full license control and more.
It has full set of API, so you can handle it by other applications as well. One app handles license of all your products. It will make the WordPress as license server.
You can license any product with any language (PHP, .Net, Java, Android, etc.). Also you can add licensing to more than one WordPress plugin or theme and it can be installed on same WordPress.