Copyleft in Deep

Copyleft to me is the opposition of copyright. So whatever comes to a common user's mind when thinking about copyright (acquisition price, closed source code, unavailability of sharing etc.), they should think the opposite when keeping copyleft in mind.


To me, copyleft classifies itself to three categories, each represented by different licenses:

1. GNU General Public License

The best of the best. Main idea is, that the freedom of the user overpowers the freedom of the developer. Whatever the developer produces, he or she has to keep in mind, that when the product one develops or re-develops is published under GPL, no form of restrictions can be made to the products source code (essence) or usage (price, geographical or even linguistic peculiarities).

Software released under GPL that is familiar to me, is for example CDex, which is a cd-ripping tool I use to digitalize my old cd's for easy listening.

2. GNU Lesser General Public License (alternative option: Mozilla Public License)

Middle-ground for the collision of GPL and BSD-like schools-of-thought. As I understand, LGPL means, that the product under development has to follow GPL principles (the good), but all the products used for the making of this under-construction product do NOT have to be GPL-implemented. Could this mean, that saome sort of e-mail arranger could be released under LGPL for Microsoft Outlook. Appears so?! Also one can use LGPL software commercially, as long as all the LGPL material and it's developments remain licensed under LGPL.

One of the most famous products using LGPL is ofcourse 7-Zip which is by far the greatest file-packer in the world. A great overview of the principles of LGPL is given by 7-zip site's developer FAQ - http://www.7-zip.org/faq.html.

3. BSD license (with multitude of alternatives)


New type of copyright for the open-source community. To me it seems to be a very simplistic way of intellectual property protection, only stating that the:

* Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
    * Neither the name of the  nor the
      names of its contributors may be used to endorse or promote products
      derived from this software without specific prior written permission.

So BSD itself doesn't say anything about the neccessity to keep the source code open and freely usable for the community.

Examples of software released under BSD are many, the most famous one being FreeBSD.