Recently I have noticed that a lot of people are confused about the term "open source" in relation to the word "free".
Open source software (OSS) is computer software where the underlying source code is made available under a license. This can allow individuals and organisations who use the software and to modify it, either to improve the software or adapt it to better meet their needs.
Open source does not necessarily mean free of charge. The term “free” commonly refers to the concept of freedom attached to open source - freedom to modify the source code. The Free Software Foundation (FSF) publishes an earlier variation of the definition where it refers to "free software" rather than OSS. The FSF definition stresses that “free” software is a matter of liberty with “free” derived from “freedom” (libre) and not from “no price” (gratis). The terms open source, free software and free open source software (FOSS) are also often used as is free / libre / open source software (FLOSS).
There are different licensing models under which FLOSS is made available. Generally the licensing conditions are intended to facilitate the ongoing re-use and wide availability of the software. In contrast, vendors of closed source, proprietary software provide only executable binary code, and not the human readable source from which that code is derived. Proprietary software vendors usually also place very specific limits on redistribution of the software.
Richard Stallman (the founder of the Free Software Foundation and the GNU project) produced the GNU manifesto back in 1985, this manifesto has four key components. These components are as follows:
1. Freedom to use or run software for any purpose and for any number of users.
2. Freedom to study how the software works. Access to any source code, technical diagrams and any other documentation.
3. Freedom to share (redistribute) copies of the software and source code.
4. Freedom to modify, adapt, improve the software according to specific needs and to share (redistribute) these modifications.
Components 2 and 4 require source code to be available because studying and modifying software without the source code is highly impractical.
Note: as stated above, OSS does not necessarily mean free of charge and may have costs attached to such projects, also the license agreement may include clauses that state that any redistribution may be charged for. Usually, these charges may include access to support packages (including phone and / or e-mail support contracts).
As an example, RedHat Inc. and SuSE provide both free and commercial versions of their Linux based operating systems, the commercial costs may include options such as extra support contracts, training programmes and industry recognised certifications.
Due to Microsoft reluctance to provide source code to the public / 3rd parties, Microsoft can not be considered as a OSS provider.
The term "free" is a bit misleading and personally, I prefer to use the term "libre" (from the Spanish "libré", ie. at liberty) instead of "free" when considering open source products and developments.
OSS should be defined as software with very few limitations on distribution or improvement.
Good examples of end-user OSS include LibreOffice, Firefox, GNU Cash, GIMP, Blender and VLC. As well as various operating systems, including FreeBSD, OpenSuSE, Debian, CentOS and Fedora.
References & Other Resources:
* Free Software Directory
* Free Software Foundation
* Wikipedia: Free and Open Source Software Packages
* Technology and Open Source Blog