Free Software and Open Source software (FOSS) are related but distinct sets of ideas, practices, and copyright licenses aimed at using copyright law to maintain public rights to use, modify, and redistribute software, rather than to lock rights away as the property of a single company or person. In both cases, the source code of programs must be made available to users along with the executable version, or in some other convenient and simple way. The best known FOSS products are the Linux operating system and the Open Office application suite. One Laptop Per Child is a non-profit that intends to make FOSS education software available to as many as a billion children worldwide. Open Voting Consortium has created a demonstration version of Open Source voting software with auditability and security designed in.

Most FOSS programs are available at no cost (one meaning of free), but the Free Software Foundation emphasizes that freedom to read and reuse code is the more important concept. That is, Free as in "Freedom", not Free as in "Free Beer".

The advantages of FOSS can include

• Greater security, since code can be inspected and tested for security holes and fixed by anyone with the appropriate skill and knowledge.
  
• Better program quality overall, since anybody is permitted to offer improvements, and anyone can test the software.
• Use in education, where students of programming and Computer Science can look at software used for real-world purposes.
• Adaptability to particular requirements, incuding translation to any language.

Of course, there are poor-quality FOSS products, so users need to check whether a program will suit their needs. In particular, FOSS products may be offered in a clearly unfinished state in order to allow those interested in using it to report bugs and ask for new features.