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. Examples of public domain software include the GNU/Linux software, 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, as would be public domain software.
You can find public domain software in a variety of locations. The UCLA library offers numerous downloads and catalogues. 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 software, and free or 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 whether you are downloading freeware or public domain software.