It somewhat depends on which algorithm you'd like to use, but if decision tree is all you need (I have seen papers that claim that "decision tree is the only machine learning algorithm one ever needs", LOL), C5.0 is an improved version of C4.5 that is only available commercially from the author's own company. (Yes, I know the website looks like it hasn't been touched since 1995, but they are still in business, LOL...)
It also looks like LIBSVM is available for commercial use, and LIBSVM is probably the first- or second-most widely used Support Vector Machine implementation (versus SVMlight). Oracle also includes SVM classification which can be used commercially provided you have the right license with them. SVM is, in most cases, far superior to decision tree, but sometimes using SVM for classification is like using a wrecking ball to kill a fly. I've seen papers that support this as well LOL.
So yeah let me know if you'd like to see any of those papers. :)