Finding right license to support open source community only. GPLv3 too strict, LGPLv3 too permissive

Question

I have created an open source library ( https://github.com/pitschr/knx-link ) that is designed to be used by other open source projects; not by end users. Currently it is licensed as GPLv3.

My main goal is that every project that uses my library must be open sourced. For me personally it doesn’t matter if the other project that uses my library is licensed on e.g. Apache-2.0 or MIT as long the project used by the end-user is open sourced on e.g. GitHub.

Based on different licenses I see that:

• LGPLv3 would not be the right choice as it allows to be linked by a proprietary software
• GPLv3 seems be too strict for me, as enforces that other software needs to be licensed as GPLv3 as well. Furthermore, GPLv3 doesn’t allow to be used by a project which is licensed under Apache-2.0/MIT
• Apache-2.0 and MIT licenses seems not be the option for me as they can be used by proprietary software directly

I could not find the right license for my purpose. Again, it is totally fine to use my library as long the end-user project/software itself is open source without enforcing that it needs to be licensed under GPLv3 as well? My main goal is to support the open source community only!

Am I alone with the idea? What is the best way to achieve? Which license would be most suitable for me?

Thank you, Christoph (who is bit confused)

Answer 1

There's two fundamentally different takes on open source licenses:

a) the permissive ones like MIT, Apache etc which - roughly speaking - don't care what happens to their sources as long as the credits are maintained and communicated.

b) And there's the more strictly open source licenses, the copy-left licenses, which want to make sure that any derivative remains also open source, most notably the GPL license.

The license is usually chosen by the (initial) authors for a reason that s/he wants the first or the latter.

As such a license as you seek might be crafted, but serves little use: A permissively-licensed project would not want to make use of a license which can only be used in open-source projects; its license was chosen particularily such that proprietary use is possible.

A project already with a copy-left license does not need such license either - it could as well use the GPL which ensures just that: be open source and stay open source.

As such, it might even be argued that a license which may be used only in an open source project already exists: the GPL. Most open source licenses are compatible with the GPL in the sense that they may be used in a GPL-licensed project (by simply changing the license to GPL for the derived / combined software - even when notable exceptions exist like the incompatibility with Apache or MPL).