HaiGan: You might want to look into some of the existing Open Source licenses. As a Perl user, I particularly like the spiritof the Perl Artistic Licence, and despite it's origins it can be used for any sort of electronic content. The GPL is popular, though it has several known flaws. Any of them, however, serve as a good basis for allowing redistribution requiring the license and copyright notices to be included with each copy given. While this doesn't force users to a certain place to download (and thus limits the amount of traffic focus) this can be overcome with things like simple support and discussion group scripts at your site to allow users to interact about your products, which provides ample opportunity to advertise the non-free stuff. Some quick modifications of Open Source licenses can easily set up a scenario in which a person could use your work as a basis for free development provided that the result remained free as well. Several OPen Source licenses have this clause already included. And it takes very little effort to include a clause or just a word or two that make it so that you can include a little 'Ad Sheet' in the package that must be distributed with the rest of the package. Of course, some people will ignore this, but some people will ignore a no-redistribution clause too. But in the case of having a fairly easy redistribution method that is acceptable and carries information you want with it, you have another advantage: propagation without use of your bandwidth. If you use an installer executable, you can even launch both the license and the 'Ad Sheet' at the end of the installation process. And you can set the license to require the installer be used to redistribute. On that line, does anyone know of a good and easy installer-maker?