Proprietary software is computer software on which the producer has set restrictions on use, private modification, copying, or republishing. Similar terms include "closed-source software" and "non-free software".

Proprietors may enforce restrictions by technical means, such as by restricting source code access, or by legal means, such as through copyright and patents.

Literal and legal meanings

Exclusive legal rights to software by a proprietor are not required for software to be proprietary, since public domain software and software under a permissive licence can become proprietary software by distributing compiled (binary) versions of the program without making the source code available. Proprietary software includes freeware and shareware.

Software distributions considered as proprietary may in fact incorporate a "mixed source" model including both free and non-free software in the same distribution. Most if not all so-called proprietary UNIX distributions are mixed source software, bundling open source components like BIND, Sendmail, X Window System, DHCP, and others along with a purely proprietary kernel and system utilities.

For some free software, the same laws used by proprietary software are used to preserve the freedoms to use, copy and modify the software. This technique is called copyleft.

Reasons for

Proprietary software is said to create greater commercial activity over free software, especially in regard to market revenues. It has also argued that proprietary software is of better quality than free software.Fact: date=October 2008

Reasons against

The free software movement's founder Richard Stallman sometimes uses the term "user subjugating software" to describe proprietary software, while Eben Moglen sometimes talks of "unfree software". The term "non-free" is often used by Debian developers to describe any software whose licence does not comply with Debian Free Software Guidelines, and they use "proprietary software" specifically for non-free software that provides no source code. The Open Source Initiative prefers the term "closed source software".

If the proprietor of a software package should cease to exist, or decide to cease or limit production or support for a proprietary software package, recipients and users of the package may have no recourse if problems are found with the software. Proprietors can fail to improve and support software because of business problems. When no other vendor can provide support for the software, the ending of support for older or existing versions of a software package may be done to force users to upgrade and pay for newer versions or migrate to competing systems with longer support life cycles or FOSS-based systems.

Semi-free software

Semi-free software, as defined by the Free Software Foundation, is software that is not free software, but comes with permission for individuals to use, copy, distribute, and modify (including distribution of modified versions) only for non-profit purposes. Such software is also rejected by the Open Source Initiative and Debian.