Opps! I forgot to mention the obvious: You can use Qt 3 widgets for free as long as you don't try to market an app made with them. If you want to market an app you should buy a license from Toll Tech. If a client installs Linux and loads KDevelop, Qt Designer and Qt 3 from the distro and uses it for themselves only, not to create and market an app, they can use the free Qt 3 too.