Take a look at these screenshots of the License Manager wordpress plugin.
Very easy to install into any WordPress site, with all license management systems running from the WordPress admin area.
The 3 config areas that you can see are:
- The Products that are being licensed,
- The Licenses that are created, both manually or automatically, and
- The License Generators ** Exclusive to CopyProtectSoftware
Gives you ultimate control over how licenses can be automatically generated for your software