Introducing Functional Source License

Sentry is a platform for monitoring application code health created a new open source license and named it as Functional Source License (FSL).

Sentry has contributed a lot to open source. They have used various types of license like BSD-3, Business Source License (BSL) for their projects. Few years back they moved most of their projects to BSL. BSL is less permissive license which makes them to create a new license.

BSD-3, MIT license are more permissive which gives more freedom but it creates problem of free riding. Customers use it but don't pay for it. Business Source License (BSL) is less permissive license, BSL gets converted to open source after 4 years of non-competitive and it also has many variable parameters. This makes each license as different. Third party users should go through it before using the BSL licensed products. Companies like MongoDB, Elastic, SurrealDB, MariaDB and few others choose BSL.

To overcome this issue, Sentry introduces Functional Source License (FSL). This is an evolution of BSL that balances user freedom and developer sustainability. In FSL, the change date is two years, after two years license can be changed to either Apache 2.0 or MIT. There is no additional use grant but it also has non-competitive clause. Third party can use the software for commercial purpose but they should not compete with the product owners. 

In plain language, you can do anything with FSL software except economically undermine its producer through harmful free-riding. You can read it, learn from it, run it internally, modify it, and propose improvements back to the producer. 

Open source developers should carefully choose license for their products. Each license terms and conditions are different. In our opinion, FSL is good for SaaS based open source products.