Can I use WEKA in commercial applications?

Since WEKA is licensed under the Gnu General Public license (GPL 2.0 for Weka 3.6 and GPL 3.0 for Weka > 3.7.5), any derivative work must be licensed under the GPL as well.

For projects that are never publicly available (like from hobbyist programmers), this has no implications. If the project, on the other hand, is publicly available, then the source code must be made available as well, next to the executable(s).

For commercial projects it is possible to obtain a commercial license through WaikatoLink the commercialization unit of the University of Waikato or Pentaho corporation. Email weka-enquiries at waikatolink.co.nz to contact WaikatoLink or Rod Squires (rsquires at pentaho.com), executive VP of worldwide sales, at Pentaho.