Open-source software is also free to use, but “free” can be applied to its use in two ways. First, it can be used at no cost for the user. We download open-source software, just as well do any software, but installation proceeds without entering account information. Second, users are free to use the software in that they can open the source code. Recall that the source code is different from the customizations that are allowed in both open-source and proprietary software.
It is important to note that open-source licenses do have copyrights attached to the titles. These licenses allow for free use (in both senses of the term) of the software, but they affect how the software can be reused. Copyleft software requires the software to remain free for any derived works. Permissive licenses allow for the original software to be included in derived works that are proprietary.
- GNU General Public License (GPL)—This is a copyleft license that requires any modified versions of the software to also be open sourced and distributed under the same license. It ensures that the software and any derivatives remain free and open. GNU stands for “GNU’s not Unix” a software package created in 1983 and that has been widely used for open-source software titles.
- Mozilla Public License (MPL)—A more flexible copyleft license that allows combined works to be distributed under different licenses while keeping the original code open.
- MIT License—This is a permissive license that allows users to do almost anything with the software, as long as they include the original copyright and license notice in any copies or substantial portions of the software.
- Apache License 2.0—This permissive license allows users to use the software for any purpose, distribute it, modify it, and distribute modified versions of the software under the terms of the license. It also provides an express grant of patent rights from contributors to users.
- BSD License—There are several variants of the BSD license, but they are generally permissive licenses that allow users to use, modify, and distribute the software with minimal restrictions. The most common variant is the 3-Clause BSD License. BSD stands for Berkely Software Distribution, a package created by the University of California at Berkely.