Documentation in PDF

Versioning

• major version every year
• minor version every 3 months
• support from relase major version 5 years

Licence

Permission to use, copy, modify, and distribute this software and its documentation for any purpose, without fee, and without a written agreement is hereby granted, provided that the above copyright notice and this paragraph and the following two paragraphs appear in all copies.

In essence, with proper copyright notices, you can use it for commercial purposes and sell it without having to pay the developer for it. This copyright notice is common to licenses based on the BSD or MIT licenses.