Open source software is a computer software released under an Open Source Initiative (OSI) license, which meets the conditions of the Open Source Definition. This allows users to use, modify, further develop the software publicly, and redistribute it in derivative or non-derivative forms. Open source software is often developed in a collaborative manner.

Main features

One of the primary features characteristic of open source software is the freedom of the user to use the software for whatever purposes, on any computer as he or she wishes, and whichever technically appropriate situation.

The user also has the freedom to have the software at his or her disposal to use it according to his or needs. This includes studying its operation, fixing its bugs, enhancing its functionality, and improving the software. The user is also free to redistribute the software to other users, which can be done either for free or for a fee, not fixed beforehand.                                                                                        

Rights and obligations

According to the OSI, open source software gives users some rights and obligations. These include the following: availability and accessibility of the source code; no royalty imposed upon redistribution; no discrimination against fields of endeavor and persons or groups; and right to modify and create derivative works.

All rights granted must also flow with redistributed versions. Users may require modified or derivative versions to be circulated as the original version in addition to patches. The license is applicable to the whole program or each part of the program. In addition, the license must not limit other software, thus allowing the distribution of closed source and open source software together.

Non-protective open source licenses

One type of open source licenses applies no restrictions on the distribution of modified works (non-protective open source licenses). This means that users can use the code in non-open source applications.

Although licensors of this type of open source license preserve their copyright, they grant every right under copyright to licensees. Academic Free License v.1.2, BSD License, MIT License, Sleepycat License, and zlib/libpng License are some examples of non-protective open source licenses.

Protective open source licenses

The second type of open source license applies such restrictions (protective open source licenses). These licenses ensure that the code will always remain open or free. Licensors of this type of open source license keep their copyright and grant every right under copyright to licensees.

However, the redistribution of the program, whether derivative or non-derivative, should be under similar license. Artistic License, GNU GPL v.2.0, GNU LGPL v.2.1, Nethack General Public License, and Python License are some examples of protective open source licenses.