The Ext.NET Pro license is appropriate if you wish to develop, sell and/or otherwise distribute closed-source proprietary applications which include Ext.NET.
Ext.NET Pro is licensed on a per developer basis. Each individual who uses Ext.NET for development purposes must obtain an Ext.NET Pro license to do so.
The Ext.NET Pro license also grants a royalty free runtime license for you to include Ext.NET Pro in your product and sell an unlimited number of copies of your product without a royalty fee, subject to the terms of the License Agreement.>
One Ext.NET Pro license is required for each developer working directly with Ext.NET in an IDE, such as Microsoft Visual Studio, Microsoft Visual Studio Express, or similar.