Source-available, viewable, shared, or read-only open-source software licenses are those that allow the code to be seen but is has restrictions on its modification, distribution and use so it makes it not eligible for FOSS.
As it allows to access the code but restricts its uses, modification or distribution, it is not considered free or open software. Because of this, I would not recommend to use the word “open” when describing this kind of software, as it may lead to confusion.
OSI warns about organizations making source-available software that pretends to be considred open source. OSI coins pejoratively this software as fauxpen software.
List of Source-available Software Licenses
Types of source-available software licenses:
- Time-limited proprietary
- Noncommercial
- Constrained source-available
The most popular source-available software licenses are BSL (time-limited), commons clause (noncommercial) and SSPL (constrained source-available).
Time-limited proprietary
Time-limited proprietary, time-based open-source or delayed open-source licenses are proprietary licenses that become open source after a specific amount of time.
The time-limited proprietary would become FOSS, but it the meanwhile it is considered source-available and proprietary software.
Time-limited proprietary licenses:
- Functional Source License (FSL)
- Business Source License (BSL)
The most popular is Business Source License (BSL).
Functional Source License (FSL)
Functional Source License (FSL) is a source-available license.
After 2 years, the license switches to Apache 2.0 or MIT.
Sentry switched from BSL to FSL in 2023.
This license is much less popular than BSL.
Business Source License (BSL)
Business Source License (BSL) is a source-available license.
It restricts its used to non-production environments or to production environments for companies under a specific amount of revenues.
After 3 years, the license switches to Apache 2.0.
The license was developed by MariaDB Corporation Ab for its proprietary product MariaDB MaxScale. Do not confuse this product with the main MariaDB product, that is FOSS under a GPLv3 license.
Terraform software developed by HashiCorp switched from Mozilla license to BSL license in 2023. CockroachDB and SurrealDB also uses GPLv3 license.
Noncommercial
Noncommercial software licenses restricts the use of the source code on commercial projects.
They are not considered FOSS, as it does not meet the “freedom to run the program as you wish, for any purpose” (freedom 0) and the Open Software Definition’s 6th criteria OSD6 “No Discrimination Against Fields of Endeavor“.
Nevertheless, noncommercial software can be freely modified and distributed, while there are restrictions on their use.
Noncommercial open-source licenses featured on this post:
- Aladdin Free Public License (AFPL)
- Commons Clause
As of 2023, the most common noncommercial license is Commons Clause.
Aladdin Free Public License (AFPL)
Aladdin Free Public License (AFPL) prevents from using the code on commercial projects, though it can be used on projects given for free.
It was designed for Ghostscript in 2000, thought this software no longer uses this license and has a AGPL instead.
AFPL is no longer a popular license, but it was one of the first source-viewable ones. Commons Clause is more popular instead to restrict the commercial use of software.
Commons Clause
Commons Clause restricts the possibility of selling software, on top of an existing open source license.
The resulting license does not meet the FOSS definition, as it limits the software use.
An example is MongoDB, that uses Apache v2.0 with a Commons Clause.
Constrained Source-available
Constrained source-available establishes restrictions on how to use, modify and distribute it.
Constrained source-available licenses:
- Server-Side Public License (SSPL)
- Oracle Binary Code License Agreement
- Elastic License
The most common is SSPL.
Server-Side Public License (SSPL)
You can read this post on SSPL.
Oracle Binary Code License Agreement
Oracle Binary Code License Agreement allows users to view source code, but prohibits modification or redistribution of the code.
Examples of Oracle Binary Code License Agreement are some implementations of the Java Development Kit (JDK) (like Oracle JDK) or JavaFX.
Elastic License
Elastic License.
When companies such as Amazon Web Services (AWS) made big bucks by offering ElasticSearch as a service, Elastic pivoted in 2021. It abandoned the open source Apache 2.0 license for the non-open source SSPL and Elastic license.
Prosperity Public License
Prosperity Public License
PostOpen
You can read this post about PostOpen.
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External References
- SSPL
- OSI Board of Directors; “The SSPL is not an Open Source License”; OSI, 2021-01-19
- Stack Exchange community; “Has FSF commented on SSPL?“; StackExchange
- Hacker News community, “I hope OSI and the FSF don’t approve their new “SSPL” license“, YCombinator
- FSL
- Richard Speed; “License to thrill BSL refuseniks? Sentry introduces Functional Source License“; The Register, 2023-11-20
- Steven J. Vaughan-Nichols; “Do we really need another non-open source available license?“; The Register, 2023-11-24