What is a copyleft license?

A copyleft license is a type of license that grants users the right to freely use, modify, and distribute a work, with the condition that any derivative works must also be distributed under the same or a compatible copyleft license. The purpose of a copyleft license is to ensure that the work and its derivatives remain freely available for anyone to use, modify, and share, promoting collaboration and preventing proprietary restrictions.

Key Features:

1. Freedom to use: Users can freely use the work for any purpose without restrictions.
2. Freedom to modify: Users can adapt, improve, or build upon the work to suit their needs.
3. Freedom to distribute: Users can share the original work and any derivative works with others.
4. Reciprocity: Any derivative works must be licensed under the same or a compatible copyleft license, ensuring that the freedoms granted by the original license are preserved.

Examples of Copyleft Licenses:

1. GNU General Public License (GPL): The GPL is one of the most popular copyleft licenses, primarily used for software. It requires that any derivative works or software that includes GPL-licensed code must also be released under the GPL.
2. Creative Commons Attribution-ShareAlike (CC BY-SA): This license is often used for creative works such as writing, art, and music. It allows users to share and adapt the work, as long as they give credit to the original creator and license their derivative works under the same terms.
3. Mozilla Public License (MPL): The MPL is a copyleft license that is more permissive than the GPL. It allows users to combine MPL-licensed code with proprietary code, as long as the MPL-licensed portions remain open source.

Comparison with Other License Types:

1. Permissive licenses (e.g., MIT, BSD): These licenses allow users to freely use, modify, and distribute the work without the requirement to share derivative works under the same license. This enables the creation of proprietary derivatives.
2. Public domain: Works in the public domain have no copyright restrictions and can be used, modified, and distributed by anyone without any obligations.
3. Proprietary licenses: These licenses restrict the use, modification, and distribution of the work, often requiring payment or specific permissions from the copyright holder.

Advantages and Disadvantages:

Advantages:

• Promotes collaboration and sharing
• Ensures that the work remains freely available for future users
• Prevents proprietary restrictions and lock-in
• Encourages the development of a community around the work

Disadvantages:

• May be less attractive for commercial use due to the reciprocity requirement
• Can lead to compatibility issues when combining works under different copyleft licenses
• Some users may find the licensing terms confusing or restrictive

In conclusion, copyleft licenses provide a unique way to ensure that a work remains freely available and open to collaboration while preventing proprietary restrictions. They have played a significant role in the development of open-source software and creative works, promoting innovation and community-driven projects.