The MySQL marketplace today is far more complex then simply choosing between a particular version of MySQL that Sun/MySQL (http://mysql.com) produces.
The MySQL server product in general is released under the GNU General Public License (GPL) v2, however you should carefully review the MySQL Legal Policies (http://www.mysql.com/about/legal/) as a number of exceptions and different license agreements operate for companion tools such as MySQL Cluster, MySQL client libraries and documentation for example.
Looking into the MySQL ecosystem for products, I’ve produced the following categories:
- Sun/MySQL Official Products
- MySQL Versions
- MySQL Variants
- MySQL Plugins