I'm looking for a licence that I could use that would allow me to distribute my projects/products (for free or a cost), and allow people to develop and customize that product. But they will not be aloud to take code/resources from the product and use it in other products.

As I'm happy sharing projects like urGallery, but not the backend that makes it work. As the backend is what I use to power my professional projects for clients. So if I release urGallery with the backend, and other developers start using the backend for their own non-urGallery work, then it would hurt my business.

Can anyone point me in the right direction?