Best LGPL-3.0 Licensed Open Source Repositories

The GNU Lesser General Public License version 3 (LGPL-3.0) is a copyleft license, but a weaker form of copyleft than the GPL. It is designed primarily for software libraries: a program that merely links to an LGPL-licensed library, without modifying the library itself, is not required to be released under the LGPL or any particular license. If the library's own source code is modified, those modifications must be shared under the LGPL when the modified library is distributed.

LGPL-3.0 incorporates GPLv3 terms for the library's own licensing, so it carries GPLv3's explicit patent grant and patent retaliation clause, along with protections against so-called "Tivoization," hardware restrictions that prevent users from running modified versions of the software. The license requires that users be able to relink a modified version of the library into the larger application, either through dynamic linking or by providing the object files and linking instructions needed to do so.

Compared to the plain GPL, LGPL-3.0 is meant to let proprietary or differently-licensed applications depend on an LGPL library without the whole application becoming subject to copyleft. Compared to permissive licenses like MIT or Apache-2.0, LGPL still imposes obligations: if the library itself is modified, those changes must be released under the LGPL, and the application must permit users to substitute their own version of the library.

Practically, this makes LGPL-3.0 common for shared libraries and SDKs meant to be used inside both open-source and proprietary applications, where authors want library-level source availability without extending copyleft to every program that links against the library.