Wow, I was gonna add to this, but after reading mmurfin87 and wmarone's comments, there's really nothing more I can add except to say that they're spot on. You can't add GPL stuff without at least a LGPL license. The only exception I know is if the modules are plugins, meaning they're optional components that just "snap in" and not physically required for the application's core functions to work. You could also get around it by having a "shim", IE, some kind of software API that was LGPL and acted as a go between for the GPL'ed code and the proprietary code. It's how Microsoft figured out how to run their apps on Linux without having to open source them, or release them under an open source license.