Open-source software is a type of software whose source code is publicly available. Individuals and companies may use the code in its original form, modify it, improve it and distribute it.
However, the fact that source code is freely accessible does not mean that there are no rules or restrictions governing its use. The rules applicable to the use of software are set out in licences.
Several different standards have developed for the use of open-source software. These standards are incorporated into different types of licences. Below, we outline some of the most common open-source licences and the principal differences between them.
GPL Licence
One of the most common open-source software licences is the GPL, or General Public License.
This licence allows users to use, copy and modify software code free of charge. It also requires users to return any modifications to the open-source community. This means that any modification of software code made available to the public under the GPL must remain subject to the same licence.
In practice, this means that if someone uses code from software licensed under the GPL and modifies it, they must make those modifications available to others.
One example of software distributed under the GPL is the Linux operating system. Because Linux is open source, anyone may use and modify its code free of charge, but modifications must be shared with other users.
Another example of software distributed under this licence is the MySQL database.
LGPL Licence
Another common licence is the LGPL, or Lesser General Public License.
This licence is similar to the GPL, but contains an important distinction regarding the publication and licensing of modifications.
Software licensed under the LGPL may be used in combination with software distributed under other licences. This means that someone may use LGPL-licensed software while licensing software that interacts with or incorporates it under different terms, including proprietary terms under which the complete source code is not made available to the public.
An example of software available under the LGPL is the Qt software development framework.
MIT Licence
Like the GPL, the MIT Licence permits the free use, modification and distribution of open-source software.
The principal difference is that a user who modifies the source code is not required to disclose or distribute those modifications to others. The modified software may therefore be incorporated into proprietary or closed-source software.
The MIT Licence is one of the simplest and most widely used open-source software licences.
An example of open-source software distributed under the MIT Licence is the React JavaScript library.
Apache Licence
The Apache Licence is similar to the MIT Licence.
It permits users to use, modify and distribute software, including for commercial purposes. Users must retain the relevant copyright, licence and attribution notices when redistributing the software.
Unlike copyleft licences such as the GPL, the Apache Licence does not generally require users to make modifications to the source code publicly available.
Creative Commons
Creative Commons refers to a group of licences through which authors and other holders of economic copyright may define how their works published online may be used and shared.
Several types of Creative Commons licences are available. They differ according to the conditions that users must comply with when using, adapting and distributing copyright-protected content.
Creative Commons licences are primarily intended for creative works and content rather than software source code. Software is generally licensed under licences specifically designed for software, such as the GPL, MIT or Apache licences.