Table of Contents
    Home / Insights / What is Open Source Software?
    Applications 11 min read

    What is Open Source Software?

    We discuss open-source software, the basics behind the Open Source Initiative (OSI), and Free Software Licensing.

    Open source refers to a program or software in which the source code (the form of the program when a programmer writes a program in a particular programming language) is available to the general public for use and/or modification from its original design free of charge. Open source code is typically created as a collaborative effort in which programmers improve upon the code and share the changes within the community.

    The Rationale Behind Open Source Software

    The rationale for this movement is that a larger group of programmers not concerned with proprietary ownership or financial gain will produce a more useful and bug-free product for everyone to use. The concept relies on peer review to find and eliminate bugs in the program code, a process that commercially developed and packaged programs do not employ.

    The basics behind the Open Source Initiative is that when programmers can read, redistribute and modify the source code for a piece of software, the software evolves. Open source sprouted in the technological community as a response to proprietary software owned by corporations.

    Contrast with Proprietary Software

    Proprietary software is privately owned and controlled. In the computer industry, proprietary is considered the opposite of open. A proprietary design or technique is one that is owned by a company. It also implies that the company has not divulged specifications that would allow other companies to duplicate the product.

    Open-source software plays a key role in enterprise security platforms. Read more at eSecurityPlanet’s Top Open Source Security Tools.

    What is The Open Source Initiative (OSI)?

    Open Source is a certification standard issued by the Open Source Initiative (OSI) that indicates that the source code of a computer program is made available free of charge to the general public. OSI dictates that in order to be considered “OSI Certified” a product must meet the following criteria:

    The Open Source Definition, by the Open Source Initiative

    Open source software is normally distributed with the source code under an open source license. The Open Source Initiative sets the following distribution terms that open-source software must comply with;


    Open source doesn’t just mean access to the source code. The distribution terms of open-source software must comply with the following criteria:

    1. Free Redistribution

    The license shall not restrict any party from selling or giving away the software as a component of an aggregate software distribution containing programs from several different sources. The license shall not require a royalty or other fee for such sale.

    2. Source Code

    The program must include source code, and must allow distribution in source code as well as compiled form. Where some form of a product is not distributed with source code, there must be a well-publicized means of obtaining the source code for no more than a reasonable reproduction cost preferably, downloading via the Internet without charge. The source code must be the preferred form in which a programmer would modify the program. Deliberately obfuscated source code is not allowed. Intermediate forms such as the output of a preprocessor or translator are not allowed

    3. Derived Works

    The license must allow modifications and derived works, and must allow them to be distributed under the same terms as the license of the original software.

    4. Integrity of The Author’s Source Code

    The license may restrict source-code from being distributed in modified form only if the license allows the distribution of “patch files” with the source code for the purpose of modifying the program at build time. The license must explicitly permit distribution of software built from modified source code. The license may require derived works to carry a different name or version number from the original software.

    5. No Discrimination Against Persons or Groups

    The license must not discriminate against any person or group of persons.

    6. No Discrimination Against Fields of Endeavor

    The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research.

    7. Distribution of License

    The rights attached to the program must apply to all to whom the program is redistributed without the need for execution of an additional license by those parties.

    8. License Must Not Be Specific to a Product

    The rights attached to the program must not depend on the program’s being part of a particular software distribution. If the program is extracted from that distribution and used or distributed within the terms of the program’s license, all parties to whom the program is redistributed should have the same rights as those that are granted in conjunction with the original software distribution.

    9. License Must Not Restrict Other Software

    The license must not place restrictions on other software that is distributed along with the licensed software. For example, the license must not insist that all other programs distributed on the same medium must be open-source software.

    10. License Must Be Technology-Neutral

    No provision of the license may be predicated on any individual technology or style of interface.

    [Source: Open Source Initiative, “The Open Source Definition“]

    Free Software Licensing

    All open source software is not distributed under the same licensing agreement. Some may use a free software license, a copyleft, or GPL compatible. The GNU GPL license is a free software license and a copyleft license, while a “GNU Lesser General Public License” is a free software license, but not a strong copyleft license. There are many different types of licenses for free software . some GNU GPL compatible, some not.

    The Open Source Initiative approves open source licenses after they have successfully gone through the approval process and comply with the Open Source Definition (above). There is currently well over fifty licenses that have been approved by the OSI.

    For example, the GNU General Public License (GPL) is one license that accompanies some open source software that details how the software and its accompany source code can be freely copied, distributed and modified. The most widespread use of GPL is in reference to the GNU GPL, which is commonly abbreviated simply as GPL when it is understood that the term refers to the GNU GPL.

    One of the basic tenets of the GPL is that anyone who acquires the material must make it available to anyone else under the same licensing agreement. The GPL does not cover activities other than the copying, distributing and modifying of the source code.

    Other open source licenses include the following:

    Academic Free License 3.0 (AFL 3.0)
    Affero GNU Public License
    Adaptive Public License
    Apache Software License
    Apache License, 2.0
    Apple Public Source License
    Artistic license
    Artistic license 2.0
    Attribution Assurance Licenses
    New and Simplified BSD licenses
    Boost Software License (BSL1.0)
    Computer Associates Trusted Open Source License 1.1
    Common Development and Distribution License
    Common Public Attribution License 1.0 (CPAL)
    Common Public License 1.0
    CUA Office Public License Version 1.0
    EU DataGrid Software License
    Eclipse Public License
    Educational Community License, Version 2.0
    Eiffel Forum License
    Eiffel Forum License V2.0
    Entessa Public License
    Fair License
    Frameworx License
    GNU General Public License (GPL)
    GNU General Public License version 3.0 (GPLv3)
    GNU Library or “Lesser” General Public License (LGPL)
    GNU Library or “Lesser” General Public License version 3.0 (LGPLv3)
    Historical Permission Notice and Disclaimer
    IBM Public License
    Intel Open Source License
    ISC License
    Jabber Open Source License
    Lucent Public License (Plan9)
    Lucent Public License Version 1.02
    Microsoft Public License (Ms-PL)
    Microsoft Reciprocal License (Ms-RL)
    MIT license
    MITRE Collaborative Virtual Workspace License (CVW License)
    Motosoto License
    Mozilla Public License 1.0 (MPL)
    Mozilla Public License 1.1 (MPL)
    Multics License
    NASA Open Source Agreement 1.3
    NTP License
    Naumen Public License
    Nethack General Public License
    Nokia Open Source License
    Non-Profit Open Software License 3.0 (Non-Profit OSL 3.0)
    OCLC Research Public License 2.0
    Open Group Test Suite License
    Open Software License 3.0 (OSL 3.0)
    PHP License
    Python license (CNRI Python License)
    Python Software Foundation License
    Qt Public License (QPL)
    RealNetworks Public Source License V1.0
    Reciprocal Public License
    Reciprocal Public License 1.5 (RPL1.5)
    Ricoh Source Code Public License
    Simple Public License 2.0
    Sleepycat License
    Sun Industry Standards Source License (SISSL)
    Sun Public License
    Sybase Open Watcom Public License 1.0
    University of Illinois/NCSA Open Source License
    Vovida Software License v. 1.0
    W3C License
    wxWindows Library License
    X.Net License
    Zope Public License
    zlib/libpng license

    [Source: You can read the details and newly added approved licenses on the OSI Open Source Licenses Web page]

    Programmers & Corporations – Why Invest in What is Free?

    A software programmer really has his or her own reasons for contributing to open source projects. Some may just be looking for fun or a challenge, while others are looking to improve skill and build on their programming abilities, or they may want to belong to a group project. In many instances there is the opportunity to make money as open source projects can be funded by government or corporate sponsors. Unlike commercial projects, open source projects allow the programmer’s name to be known, which benefits a programmer’s name and portfolio which can lead to future jobs with other funded open source or commercial projects.

    The hype and benefits of open source has not gone unnoticed in the commercial world where some corporations have jumped on the open source bandwagon. Since commercial software is sold for profit, one may wonder why a company would be interested in open source projects. In many cases companies are able to profit through selling add-on tools or modules, or paid consulting services and technical support for the program.

    Some Successful Open Source Projects


    Sendmail is an open source mail transfer agent (MTA) used for routing and delivery e-mail. The original version of Sendmail was written by Eric Allman in the early 1980s. It is estimated that Sendmail is installed on 60 to 80 percent of the Internet’s mail-server computers.

    Apache Web server

    Often referred to as simply Apache, a public-domain open source Web server developed by a loosely knit group of programmers. The first version of Apache, based on the NCSA httpd Web server, was developed in 1995. Core development of the Apache Web server is performed by a group of about 20 volunteer programmers, called the Apache Group. However, because the source code is freely available, anyone can adapt the server for specific needs, and there is a large public library of Apache add-ons.


    (Pronounced lee-nucks or lih-nucks). A freely distributable open source operating system that runs on a number of hardware platforms. The Linux kernel was developed mainly by Linus Torvalds. Because it’s free, and because it runs on many platforms, including PCs and Macintoshes, Linux has become an extremely popular alternative to proprietary operating systems.


    Acronym for GNU Network Object Model Environment. (Pronounced guh-nome) GNOME is part of the GNU project and part of the free software, or open source, movement. GNOME is a Windows-like desktop system that works on UNIX and UNIX-like systems and is not dependent on any one window manager. The current version runs on Linux, FreeBSD, IRIX and Solaris. The main objective of GNOME is to provide a user-friendly suite of applications and an easy-to-use desktop.

    Key Terms To Understanding Open Source

    open source
    Generically, open source refers to a program in which the source code is available to the general public for use and/or modification from its original design free of charge, i.e., open.

    Short for General Public License, the license that accompanies some open source software

    Self-referentially, short for GNU’s not UNIX, a UNIX-compatible software system developed by the Free Software Foundation (FSF).

    Pronounced lee-nucks or lih-nucks. A freely-distributable open source operating system that runs on a number of hardware platforms.

    Read more on Linux history, apps, operating systems, and more at LinuxToday.

    Acronym for GNU Network Object Model Environment. (Pronounced guh-nome.) GNOME is part of the GNU project and part of the free software, or open source, movement.

    Did You Know… The Open Source Definition was written by Bruce Perens as “The Debian Free Software Guidelines”, and refined it using the comments of the Debian developers in a month-long e-mail conference in June, 1997. He removed the Debian-specific references from the document to create the “Open Source Definition.”





    Was this Article helpful? Yes No