You can build "on top" of GNU software. You just can’t include their software in your program. Your software must be separate from theirs. You can link to libraries, access databases, etc but cannot compile their code into yours. If you do, then you should make your code available under the same GNU license.
You can build "on top" of GNU software. You just can’t include their software in your program. Your software must be separate from theirs. You can link to libraries, access databases, etc but cannot compile their code into yours. If you do, then you should make your code available under the same GNU license.