Mozilla Public License

The Mozilla licence was developed originally for the mozilla project. It differs from other projects, and more closely reflects my redistribution wishes, in the following ways.

Similar to the LGPL, it allows incorporation into closed source software, but the part that is kept open source and requires redistribution to the community is based on a programming unit, usually a class, or possibly a header file. Thus it does not require arbitrary division of the program into libraries. This is particularly important in this case, as it would allow someone to attach a closed source library to this program (rather than the other way round).

http://www.mozilla.org/MPL/MPL-1.1.html