Understanding Open Source Licenses in Free and Open Source Software (FOSS)
FOSS represents a philosophy of openness, collaboration, and freedom in software development. It helps developers and users to access, modify, and share software freely. However, these freedoms are governed by licenses that define the rules for usage, modification, and redistribution. Open source licenses are essential for protecting intellectual property while fostering innovation and collaboration. They fall into two primary categories: Copyleft and Permissive licenses. Each type has unique characteristics that influence how software can be used and distributed.
Copyleft Licenses
Copyleft licenses are designed to ensure that software remains free and open for all users. They impose conditions requiring derivative works to be distributed under the same license terms as the original software. This approach guarantees that the freedoms granted by the original software persist in all modified versions.
GNU General Public License (GPL)
The GPL is one of the most influential copyleft licenses. It requires that any software incorporating GPL-licensed code must make its source code available under the same GPL license. This ensures that derivative works remain open source, preserving transparency and freedom. However, the GPL’s strict requirements can deter commercial use or integration with proprietary software, as companies may not want to disclose their proprietary code when using GPL-licensed components.
The GPL also includes provisions to prevent "tivoization," where hardware manufacturers lock down devices to prevent users from modifying the GPL-licensed software running on them. This makes the GPL particularly appealing for projects aiming to protect user freedoms in embedded systems or consumer electronics.
Affero General Public License (AGPL)
The AGPL extends the principles of the GPL to address a specific loophole: software accessed over a network but not explicitly distributed. For example, web applications that use open source code do not traditionally fall under standard GPL requirements because they are not "distributed" to end users. The AGPL closes this gap by requiring developers to provide access to the source code of applications running on a server if they interact with users over a network. This makes it ideal for web-based applications and cloud services where transparency is critical.
Lesser General Public License (LGPL)
The LGPL is a more lenient version of the GPL designed specifically for libraries. It allows LGPL-licensed libraries to be linked with proprietary applications without requiring the entire application to be open source. This makes it suitable for developers who want their libraries to be widely adopted while still maintaining some level of openness. However, any modifications made directly to the LGPL-licensed library itself must be shared under LGPL terms.
Eclipse Public License (EPL)
The EPL is another copyleft license but with a focus on balancing openness with business-friendly terms. It permits combining EPL-licensed software with proprietary code as long as they remain separate modules. Any modifications made directly to EPL-licensed code must be released under EPL terms, but proprietary extensions can coexist alongside it without restrictions. This makes the EPL popular among enterprise developers who need flexibility when integrating open source components into their products.
Mozilla Public License (MPL)
The MPL offers a middle ground between permissive and copyleft licenses. It allows MPL-licensed code to coexist with proprietary software as long as MPL-licensed files remain separate and are distributed alongside proprietary components. Developers can modify MPL-licensed files freely but must release those changes under MPL terms. This flexibility makes it appealing for projects that require both openness and compatibility with proprietary systems.