It is licensed under Apache so the answer is no. If you are interested, you can read the license agreement on Apache.
http://www.apache.org/licenses/LICENSE-2.0.html


On Tue, Nov 6, 2012 at 10:35 AM, Manuel Alejandro Ortiz Gil <manuel24ortiz@gmail.com> wrote:
Hi, I want to use Cassandra for a website and want to know if i have to pay any right to use it.