Proprietary software is software that has restrictions on using and copying it, usually enforced by a proprietor. The prevention of use, copying, or modification can be achieved by legal or technical means. Technical means include releasing machine-readable binaries only, and withholding the human-readable source code. Legal means can involve software licensing, copyright and patent law. Proprietary software can be sold for money as commercial software or available at zero-price as freeware. According to the Free Software Foundation (FSF), proprietary software is any software that does not meet its definitions of free software or semi-free software. The term's literal meaning covers software that has an owner who exercises control over the software. This could include any software that is not in the public domain, including free software with existing copyrights. The FSF asserts that the restrictions of free software offer computer users freedom while the restrictions of other software benefit only the owner and are "unethical". The adjective "proprietary" also avoids confusion with the phrase "commercial software", since free software can also be sold and used for commercial purposes.

If for any reason the proprietor ceases, or decides to cease, or limit production or support for a proprietary software product, previous licensors can be left at a disadvantage and have no recourse if problems are found with the software.

The term "non-free software" (or "nonfree") is used interchangeably and about as often by the free software movement. FSF founder Richard Stallman sometimes uses the term "user subjugating software", while Eben Moglen sometimes talks of "unfree software". The term "non-free" is generally used by Debian developers, but they too sometimes talk of "proprietary software". The Open Source Initiative prefers the term "closed source software".

Some free software packages are available under proprietary terms. Examples include MySQL, Sendmail and SSH. The original copyright holders for a work of free software, even copyleft free software, can use dual-licensing to allow themselves or others to redistribute proprietary versions. Non-copyleft free software, or free software "with a permissive license", allows anyone to make proprietary redistributions.

Some proprietary software comes with source code or provides offers to the source code. Users are free to use and even study and modify the software in these cases, but are restricted by either licenses or non-disclosure agreements from redistributing modifications or sharing the software. Examples include Pine, the Microsoft Shared source license program, and certain proprietary implementations of SSH.

Like freeware, shareware is proprietary software available at zero price for a trial period. Proprietary software that has a copyright that isn't enforced but is used illegally by users is called "abandonware" and may include source code. Some abandonware has its source code placed in the public domain either by its author or copyright holder and is therefore free software, not proprietary software.

Well known examples of proprietary software include Microsoft Windows, RealPlayer, Adobe Photoshop, Mac OS, WinZip and some versions of UNIX.

See also

• Non-proprietary software
• Software hoarding
• Vendor lock-in

References