Free or Open Source Software (FOSS) refers to software that is available for use in the Source Code form.
Applications can be downloaded for free, thus making them readily available to a wide audience at practically no cost.
In addition, Open Source Software runs on the Apache Web Server, which in turn runs on Windows, Linux, Solaris, and various other UNIX platforms.
Since licenses are open there are hardly any restrictions on the use or redistribution of the software, and the deployment of apps based on Open Source technology.
Using open source applications and pre-packaged PHP modules for application development can save around 30% - 40% of the development time.
With Open Source you are not affected by the restrictions imposed on the use of proprietary or commercial software.