”Unfortunately” it is also necessary to retain licenses in the world of Open Source software. However these licences relate more to what one is free to do that what limitations are imposed.

The licenses are also intended for those who write or contribute to the program, so that they can define how their product will be handled in future.

Here we briefly define the most common Open Source software licenses: GPL and BSD.

For a comprehensive list of licenses with explanations, please see the Free Software Foundation’s list.

GPL

Over half of all Open Source software is licensed under GPL (GNU Public License). The most well known is perhaps the Linux operating system, with which it has become particularly associated. Even though the majority of programs that are licensed under GPL belong to the Unix family (of which Linux is a part), a number of programs or program editions for non-Unix systems, for example Microsoft Windows, are stating to appear.

The chief principle behind the GPL licence is pure and simply that the source code should be open and easily accessible for the user so that the user has the potential to change the code to suit his needs.

BSD

Unlike the GNU General Public Licence, the BSD licence (from Berkely Software Distribution, which was originally the name of the UNIX versions created by the University of California in Berkeley) permits the user to reuse the source code without passing on the changes. This means that work based on BSD licensed software may be issued as proprietary software. Microsoft has made use of this and used the network code for BSD in Windows. Another example is the many Free BSD components in Max OS X.

It is possible to distribute software under both the BDS licence and another licences. This was the case with previous versions of BSD Unix, which included producer owned (proprietary) material from AT&T.

Source: The content here is based on information from Linuxguiden.