Many of the desktop applications we review and recommend fall into the category of open source. Let's take a look at what that means. Open source is a movement in software, a way of licensing software and a business model. Most important for the way we use it and recommend it -- it means the software is available to users at "no charge" and can be freely copied and shared unlike commercial software like say Microsoft Office. Some of the other interesting aspects of open source is that the source code is normally available and can be modified by other developers who might want to create another application based on the original. Anything that is created from the original software should also be licensed the same as open source. The license must not discriminate against persons or groups, it can't be specific to a particular product or platform. That doesn't mean it has to be built for every platform but it has to be available to be written for any platform.  It can originally be built for Windows but it can't be restricted to not run on Mac. One of the most interest aspects of open source is that the software is often developed by projects of communities of developers who may be distributed around the world and my never meet in person. They build the software for the love of the technology and trying to achieve excellence. Some famous and successful open source include the operating system Linux, the office suite Open Office and the browser we all like to use Firefox. Open source is a concept well worth supporting because it produces excellent accessible software and is available at a great price. Optional Reading This is the full definition from the Open Source Initiative that is generally used for saying what software is and isn't open source. Introduction

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.