CDR-Stats is licensed under the AGPL version 3, and Star2Billing have also chosen to distribute this application free of charge as well.
However, there are certain rights, responsibilities and obligations that come with a product licensed under the AGPL which may be incompatible with the intended use of CDR-Stats in a commercial environment; e.g. wherever the copyright and license is displayed, so must it be displayed on your modified version, and you must make a copy of your derived application freely available (free as in cost and license).
For instance, a company may perfectly reasonably want to make a derivative proprietary commercial application from CDR-Stats, which they do not want to release under the AGPL free of charge; or indeed, make CDR-Stats part of a larger application with a license incompatible with the AGPL.
In this case, you would have the option of purchasing a commercially licensed version, identical to the free version, but with the right to modify CDR-Stats in whichever way you wish, and incorporate it into your own products and services without the obligations required by the AGPL.
The cost of a commercial license for CDR-Stats start at €500 Euro, and we would appreciate a free copy of your derivative product, but this is not compulsory.
For more information, please contact sales@star2billing.com