WEEK 6. Copyleft

Choosing the correct license or understanding what rights a certain license provides me with has always been a tricky task for me. Often such ignorance can put a person in a trouble of legal kind. The term "copyleft" is new to my ears and I am grateful for this week's topic. It has sorted things out in my head and now I feel way more secure in this field.

Copyleft can be presented in either of the three forms:

Strong copyleft

Restricts the license type of derived product to match the one of the original. Thus, such derived software cannot be made proprietary and makes it challenging to use the strong copyleft software as a library. One of the examples of software with strong copyleft would be Telegram (Telegram for Android license). The application is shipped under GNU General Public License v2.0. The source code of the app is open, any modifications can be made. The derived software must be shipped under the same license.

Weak copyleft

Weak copyleft is perfect for libraries. While still enforcing licenses for derived products, it doesn't dictate rules for apps-integrators (here I make a difference between software which is build on top of another one and software which integrates another software just as a tool). One example of a solution using weak copyleft would be LibreOffice. It uses MPLv2.0 license.

No copyleft

This type of copyleft is the friendliest for developers and places no restrictions on the license of the product that uses or inherits the original software. There are millions of libraries which would serve as an example to this copyleft type, so I will just bring up the one I interacted with the latest: Readium-sdk library for epub parsing on the Android platform. It uses BSD 3-Clause license with no copyleft.