There are two different editions of MySQL Workbench at this point in time - an open source edition and a standard edition that is only available for paying customers.
This means that MySQL Workbench introduces a new concept for MySQL. Until now, MySQL products have either been open source or only available through a commercial subscription (such as MySQL Enterprise Monitor).
MySQL Workbench is the first MySQL product that will be offered in several different editions. For those interested in the logic of this decision, please read Mike Zinner's post that may help you better understand. Mike compresses the difference as follows:
If you are a MySQL expert who has the knowledge and time to manually perform some steps, MySQL Workbench OSS will be the ideal choice for you. If you want to be able to do more in less time, you would like to have the additional safety-net or you simply want to give something back to the MySQL team - the Standard Edition is your logical choice.
The open source edition of MySQL Workbench is a fully featured, non-crippled database schema designer.. The open source edition is the code base the commercial edition is built on. It has the full feature set that is needed to efficiently design database schemata and is not crippled in any way. The commercial editions only adds modules to the open source edition to help the user save time.
The commercial edition of MySQL Workbench adds a number of advanced modules that help users to work more efficiently with the tool. These modules range from workflow optimizations to extended object handling. But you cannot buy it just yet. Commercial editions of MySQL Workbench will only be offered when they have reached production quality. The Standard Edition will be available on the MySQL online shop. Until then we welcome people joining the Beta Testing Program. If you are interested please email workbench at mysql dot com, and interact with the Workbench developers on the Workbench Forum and IRC channels.
Finally, we expect to be able to create a contributor community around MySQL Workbench. Regardless if you submit a patch for a bug or a new plugin to automate a given task - all users of the MySQL Workbench will benefit from your contribution. And in return you will benefit from the work that has done by other community members. You can start by reporting bugs and answer questions on the Workbench forum. And avid members of the MySQL Workbench community get a copy of the Standard Edition in return.
MySQL Workbench will be available on Windows, Linux and OS X. However, the first release will be on the Windows platform only. Support for other platforms will be added in a short time frame due to the clear separation of back-end and front-end code. Linux and OS X will benefit from the stabilized back-end code and are treated as first class platforms.
Condensed version: MySQL Workbench is a database design tool ready for you to download!