1. Freeware, Shareware, and Public Domain

2. Freeware
"Freeware" generally means the software is available at no charge.
Freeware is not necessarily in the public domain; the author may choose to give it away for free but wish to retain copyright to prevent it from being sold by a third party
Typically, freeware programs are small utilities or incomplete programs that authors release for their potential benefit to others, but without support.
Skype, Yahoo Messenger, Adobe Reader, IMGBurn

3. Shareware
"Shareware" is software in which the copyright is retained by the author, who intends to charge some (usually modest) amount for it, but users are allowed to try the software to see if it meets their needs before paying for it.
Shareware software is distributed at low (or sometimes no) cost, but usually requires payment and registration for full legal use.
Copies are distributed on a trial basis.
Order forms or advertisements included in the program or on the distribution disk usually tell you how to register the program and what fee is required.
Registered users of a shareware program will typically receive a printed manual, an updated copy of the software, often with additional features, and the legal right to use the program in their home or business.
Shareware is not free software, since authors of shareware programs expect payment from those who intend to use the programs regularly.
Shareware is generally written by individuals or small companies
While shareware may be freely copied, companies may not charge fees for copies that significantly exceed their duplication and handling costs.
The authors of shareware programs also retain their copyright on the contents, and you may not modify such programs or distribute modified copies.
Winzip, Cuteftp, Getright

4. Public domain Public domain software is free is available at no cost
Public domain software is not copyrighted.
It is released without any conditions upon its use, and may be used without restriction.
This type of software generally has the lowest level of support available.