How can I build custom module that can later be useful in other DNN websites.
Is this possible to fulfill this requirement in module development?
As of this point in time there is no API for you to do this automatically, but you are more than able to add your own licensing process to make this happen.
There are two concepts here that should be clarified.
Installation - taking a module and making it available to be used on a DNN site. Typically this is done via a .zip package and the module installation wizard, but there are other ways to make a module available to site. A module can be installed at the Admin (portal) level which means it can only be used in that specific portal, or it can be installed at the Host level which means it can be used on any portal.
Module Instance - once a module is installed it can be added one or more times to one or more pages. Each time a modules is added, an additional module instance is created. It is possible to share a single instance in multiple locations.
A "normal" module is unrestricted. It may be installed at the Admin or Host level and an infinite number of instances may be created throughout the portal(s). There is nothing in the framework to restrict the installation or instances of a module. Each module developer is left to provider their own commercial licensing mechanism.
This sounds more a licensing issue rather than one of functionality. You can consider each of these as different editions of your module. If you integrate the module with a DNN licensing solution such as Licence Master, you can control which features of the application are "switched on" in each of the different editions.
