Non-Free Software Licenses: Source-Available vs. Open Source
In the world of software development, there is a critical distinction between open-source software and source-available software. While both may allow a user to view the underlying code, not all licenses that provide source access are "free." To be officially recognized as open-source, a license must meet the standards set by the Open Source Initiative (OSI) and the Free Software Foundation (FSF).
Non-free licenses are those that impose restrictions—such as prohibiting commercial sale, limiting production use, or restricting redistribution—that prevent them from meeting these global standards. These licenses are often used by companies to protect their commercial interests while still allowing transparency or community review.
Key Facts
- Source-available does not mean open-source; it simply means the code is viewable.
- Non-free licenses often restrict commercial exploitation or the selling of the software.
- Some licenses use a "delayed" model, where code becomes open-source after a specific period.
- The Open Source Initiative (OSI) and Free Software Foundation (FSF) are the primary bodies that define what constitutes a "free" or "open" license.
Common Non-Free and Source-Available Licenses
The Commons Clause
Created by Fossa, Inc., the Commons Clause is an addendum added to existing open-source licenses. Its primary purpose is to restrict users from selling the software. Because of this restriction, any software using this combined license is considered source-available rather than open-source. A notable example occurred on August 22, 2018, when Redis Labs moved some Redis Modules from the GNU Affero General Public License to a combination of the Apache License 2.0 and the Commons Clause.
Business Source License (BSL)
Introduced by MariaDB Corporation in 2016, the BSL is a popular "delayed open source" license. It prohibits the use of the code in production environments unless a commercial license is purchased. This allows the author to monetize the software while eventually releasing it to the public.
Functional Source License (FSL)
Launched by Sentry in November 2023, the FSL serves as a simpler alternative to the BSL. It prohibits "competing" uses of the code to ensure the author can economically exploit their work. However, this restriction is temporary; after a limited time, the code transitions to a fully open license, such as the Apache or MIT License.
Server Side Public License (SSPL)
The SSPL is a modification of the GNU Affero General Public License created by the MongoDB project. It specifically targets software offered as a service over a network. If SSPL-licensed software is part of a service offered to others, the provider must release the source code for the entirety of the service, including all necessary APIs. Due to these discriminatory conditions toward commercial use, the OSI, Debian, and Red Hat consider it non-free.
Specialized and Proprietary Licenses
- GitLab Enterprise Edition (EE) License: Used for GitLab's commercial offerings, this license makes the product proprietary and closed source. GitLab follows an open core model, offering a separate Community Edition under the MIT License.
- Open Compensation Token License: Created by the German company iunera, this license uses blockchain technology to register code tokens. Commercial use requires a license fee calculated as a percentage of invested work hours, which is then distributed to contributors via the blockchain.
- Mega Limited Code Review Licence: Released by Mega Ltd. in 2016, this license permits the use of code strictly for "review and commentary" purposes.
- Microsoft Shared Source Initiative: Launched in May 2001, this initiative includes five licenses. While two are open-source, three are restricted: the Microsoft Limited Public License (Ms-LPL), the Microsoft Limited Reciprocal License (Ms-LRL), and the Microsoft Reference Source License (Ms-RSL).
Historical and Niche Examples
Several other licenses have faced scrutiny or evolved over time. The SugarCRM Public License was once criticized by OSI president Michael Tiemann for being "badgeware," as it required a badge to be displayed in the user interface. SugarCRM eventually transitioned to the GPLv3 in 2007 and AGPLv3 in 2010.
The TrueCrypt License was rejected by the OSI for being incompatible with the Open Source Definition (OSD) and criticized by the FSF for restricting who could execute the program. Similarly, the Old Scilab License (prior to version 5) forbade the commercial redistribution of modified versions before switching to the GPL-compatible CeCILL license.
Finally, the BeeGFS EULA allows the company to claim their software is "Open-Source" because the code is public, but the license actually prohibits distributing modified versions or using certain features without authorization.
License Summary Table
| License Name | Primary Restriction | Key Characteristic |
|---|---|---|
| Commons Clause | Prohibits selling the software | Addendum to open-source licenses |
| Business Source License | Prohibits production use | Delayed open source |
| Functional Source License | Prohibits competing use | Limited-time restriction |
| SSPL | Requires full service source disclosure | Targeted at cloud service providers |
| GitLab EE | Proprietary/Closed source | Open core business model |
| Open Compensation Token | Requires blockchain-based payment | Contributor-based compensation |
Frequently Asked Questions
What is the difference between open-source and source-available?
Open-source software must follow specific guidelines (like those from the OSI) that allow anyone to use, modify, and redistribute the software for any purpose. Source-available software allows you to see the code, but the license may restrict how you use, modify, or sell it.
Why would a company use a non-free license?
Companies often use non-free licenses to prevent competitors from taking their code and selling it as a managed service (as seen with the SSPL) or to ensure they can monetize their work while still allowing the community to review the code.
What is "delayed open source"?
Delayed open source, such as the Business Source License (BSL) or Functional Source License (FSL), is a model where the software starts under a restrictive license but automatically converts to a fully open-source license (like Apache or MIT) after a set period of time.
What is an "open core" company?
An open core company provides a basic version of their software under an open-source license (the "core") while offering a separate, proprietary "Enterprise Edition" with additional features under a non-free license, as seen with GitLab.
Why is the SSPL considered non-free?
The Server Side Public License is considered non-free by the OSI and others because it contains conditions that are viewed as unduly discriminatory toward commercial users, specifically requiring the release of all surrounding infrastructure code if the software is used in a service.