Public domain software may be software that has no copyright or whose copyright has expired. The developers of public domain software waive royalties, but the rights and source code remain the property of the authors. With some Public Domain software the source code is however supplied.
Public domain software is distributed via electronic media as well as via compact discs and DVDs that accompany print media. The difference between public domain software and shareware is that shareware is first delivered only in a reduced version and as soon as the user gets the full version, the shareware author gets licenses.