Open source licences can be a source of some confusion. Not all open source software is distributed under the same type of licensing agreement.
Common types of open source licences
Open source licences give you free access to the source code of an application, and the ability to edit, modify and share this code without seeking special permission. There are many different licences available. They can vary considerably in their legal requirements.
Most common licences are:
1. GNU General Public Licence (GPL) – The GPL grants and guarantees a wide range of rights to developers and allows users to legally copy, distribute and modify the software in any way they wish to, under certain conditions. For example, the GPL includes a restriction that any copies or derivative work must be royalty-free and imposes certain requirements for redistribution. Find out about the GNU GPL.
2. Lesser GPL Licence (LGPL) – The LGPL grants fewer rights to a work than the standard GPL. It also lets you mix elements of open source software with new proprietary applications, without making the whole application publicly available. Read more about the LGPL.
3. Berkeley Standard Distribution Licence (BSD) – BSD licences are permissive, free software licences with even fewer restrictions on distribution compared to other open source licences such as the GPL and the LGPL. However, BSD includes a template copyright notice and disclaimer which must be displayed at all times when using the software. The two variants of BSD licence are the 'simplified' or 'free BSD licence' and the 'modified' or '3-clause BSD licence'.
4. Dual licences - If you're planning on building open source tools into software and selling it, it's worth looking for software that comes with dual licences - an open source version and a paid-for version that lets you keep any changes you make. The commercial licence releases businesses from the requirement to make changes to the software open source.
Difference between copyleft and copyright licensing
Proprietary software developers use copyright to take away the users' freedom to reproduce, modify or distribute copies of their work.
In contrast, copyleft aims to give users the freedom to use, change and redistribute the software as they wish. It also requires that all modified and extended versions of the material remain freely available as well.
Open source software licences can be either copyleft or non-copyleft. The GLP is considered the most popular copyleft licence, while the BSD is an example of a copyrighted licence.
Complying with the terms of the licence
It's important to ensure that you comply with the licence associated with the software you're using - especially if you're making your own changes to the software.
The Free Software Foundation works to protect the rights of free software users and developers, can investigate businesses that breach licence terms.