by Jeremy Malcolm, Internet lawyer
A number of clients of mine who write computer software have sought my advice about the use of open source software licences, which can enable their software to be used and modified freely by users all over the world. Popular examples of open source software available for Microsoft Windows, Macintosh and Linux platforms includes the Mozilla Web browser and the Openoffice.org office suite, as well as many niche applications such as Blender for 3D graphics and BitTorrent for distributed file sharing.
Clients of mine are particularly interested in learning how to open source their software while retaining the ability to make money from it. This comes down to a decision between the different open source software licences.
The GNU General Public License (GPL) allows users to distribute the software, as well as to modify it and to distribute their modifications, so long as they make the source code freely available at the same time. This condition is what is said to make the GPL "viral", in that it requires anyone who writes software based on GPL software to release it under the GPL also.
Can you make money out of GPL software? Well yes, although it generally requires that you charge extra for support, or for customising the software to a customer's requirements, of for additional components of the software. The GPL is a popular choice for developers because it prevents others from unfairly profiting from their work. Another licence that is similar in this respect is the Mozilla Public Licence (MPL).
In distinction to the GPL are various licences that lack the same "viral" capacity to infect proprietary software. The GNU Lesser General Public License (LGPL) is similar to the GPL except that it allows proprietary software to be linked with it, without requiring the end result to be open sourced. The BSD licence is even more liberal, in that it allows the software to be relicensed in whole or in part under a proprietary licence.
The advantage of non-viral licences is that software so licensed is suitable for developers of software to use in their own work. However it is unsuitable for those who would like to open source their software and prevent others from creating proprietary versions of it. It is perhaps for this reason that viral licences such as the GPL have proven the most popular among business clients of mine who have released software of theirs under open source terms.