The Free Software Foundation has published a new open-source software licence designed for software-as-a-service (SaaS) applications.

The new licence, the GNU Affero General Public Licence version 3 (GNU AGPLv3), allows them to guarantee that modifications to software used to power publicly available services will be contributed to the free software community. It's based on the latest, third version of the GNU general public licence (GPLv3), which was finalised in June.

The GNU GPL lies at the heart of the free software movement, whose advocates contend that program source code should be freely available to study and modify. Programs released under the GNU GPL can be copied and redistributed. Developers, however, are free to modify source code and not share the changes if the software is only used inside a company.

The GNU GPL mandates that people who distribute applications built from modified source code also release the changes, but the provision didn't always cover SaaS applications, which have grown in use over the last few years. In those situations, a developer could offer a service based on a modified application without actually distributing it.

Other open-source licences have been developed that incorporate ideas similar to the GNU GPL.

Affero, a private company in San Francisco, had created a licence based on version two of the GNU GPL to accommodate SaaS. Affero said it wrote its own licence since it didn't want to wait until the GNU GPLv3 was finished.

SaaS applications are often located on servers in data centres and used for services such as email. Users can access the applications over the Internet via a web browser and further software isn't required on the PC.

The arrangement means that applications are easier to update and cheaper to run, which appeals to IT administrators.