Open-sourcing is the act of releasing previously proprietary software under an open source/free software license.

Notable software packages which have been open sourced include:

• Netscape Navigator, the code of which became the basis of the Mozilla and Mozilla Firefox web browsers
• StarOffice, which became the base of the OpenOffice.org office applications suite
• Global File System, was originally GPL'd, then made proprietary in 2001(?), but in 2004 was re-GPL'd.
• SAP DB , which has become MaxDB, and is now distributed (and owned) by MySQL AB
• InterBase database, which was open sourced by Borland in 2000 and presently exists as a commercial product and an open-source fork (Firebird)
• Doom, which now has several source ports such as Doom Legacy and lsdldoom

Before changing the license of software, distributors usually audit the source code for third party licensed code which they would have to remove or obtain permission for its relicense. Backdoors and other malware should also be removed as they may easily be discovered after release of the code.