Best MPL-2.0 Licensed Open Source Repositories

The Mozilla Public License 2.0 sits between permissive licenses like MIT and strong copyleft licenses like GPL. It applies copyleft at the level of individual files rather than the whole project: if you modify a file that's under MPL-2.0 and distribute it, that file must stay under MPL-2.0 and its source must be made available. But you're free to combine MPL-2.0 files with proprietary code in the same larger program, and those other files can stay under whatever license you choose, including closed-source. This file-level approach is why MPL-2.0 is often called 'weak copyleft' or 'file-level copyleft', and it's a deliberate middle ground between GPL's whole-project copyleft and MIT's no-copyleft approach.

MPL-2.0 also includes an explicit patent grant: contributors license any patents covering their contributions to users of the software, and that grant terminates if you sue over patent infringement related to the code. The license was rewritten in its 2.0 revision specifically to improve compatibility with other licenses, including a built-in mechanism allowing MPL-2.0 code to be relicensed as GPL or LGPL when combined with GPL-licensed software, which the original 1.1 version made difficult.

Projects choose MPL-2.0 when they want some guarantee that direct changes to their code stay open, without forcing every application built around it to become open source too. This makes it a reasonable fit for libraries and components meant to be embedded in both open and closed products. Helix, the modal text editor featured on this page, is licensed under MPL-2.0.