Initial developer permits us to do whatever we want with the code: use it, sell it, rebrand it, modify it, but always under the same conditions of the license
Contributor permits us to do whatever we want with their MODIFICATIONS: use them, sell them, rebrand them, modify them, but always under the same conditions of the license
since both previous points impose that the user MUST not suffer any change in their liberties. This point makes it incompatible for the MODIFICATIONS to have a
GPL license because the whole work would be affected
we HAVE THE OBLIGATION of giving ALL our MODIFICATIONS in source code, we can not encrypt them nor change their license
if we do a larger work, the VPL code described above cannot be restricted, in other words, anybody MUST have access to original code and ALL it's MODIFICATIONS
we MUST detail all code modifications
the code can be dual-lincesed but only vtiger can do that
“Modifications” This is a very important definition, as it specifies precisely what code you write must be made available and what you can keep proprietary.