Public domain software refers to software that is not limited by having a copyright. It can thus be freely used, copied, or altered, because no one owns the rights to restrict its use. There are plenty of public domain programs, but these are often confused with several other types of software, called freeware, which can be obtained for free, or shareware, which is usually obtained for a very small fee. Public domain software is the only type in most cases to which no limitations apply. Freeware may be copyrighted and shareware certainly is. This means it is not essentially in the public domain. Someone else can’t reproduce the software, copy it for other people, or copy it to sell without violating copyright laws.
The public domain is a large overview term for any thing, usually a creative work, that can be freely used. For example, the Bible is a public domain work. It can be used, copied, sold, quoted, translated, or altered without infringing on anyone’s copyright or patent privileges. An examples of public domain software is GNU, which forms a part of many PC operating systems.
While you can find lists of public domain software, you are more likely to find lists of free software. In most cases, this software is not really in the public domain. Your obtaining it means that you have acquired a license to use it. If you’ve ever installed a computer program for free, you probably had to accept terms and conditions for using the software. Some of these terms you agree to may prohibit you from selling, altering, or profiting from the software in any way.
There are a number of free software programs that are not public domain software. For example you can easily get copies of Adobe® Reader®, Netscape®, Internet Explorer® and a variety of other programs. Also, when you purchase a computer, you may be given several free programs, but again these are licensed to you only, rather than being yours to copy or distribute.
You can find public domain software in a variety of locations. A few college and university libraries offer downloads and catalogs. Some of the most interesting public domain software is key to the sciences. Programs like WebLab and Visual Molecular Dynamics allow you to create three-dimensional drawings of molecules. A great place to look for public domain and free software and shareware is the Free Software Foundation (FSF). You’ll find lists of public domain software, and any software that grants you automatic licenses to use specific programs. The FSF is also specific in telling you what kind of software you are downloading.