Public Domain software is software made available by its author and given free of charge. Freeware is programming offered at no cost, but it copyrighted so you may not incorporate it into anything you are developing. Postcardware is freeware that requires a user to send the software provider a postcard as a form of payment. This notifies the author that someone else is sharing the software and interested in actually using what the author has created. Shareware is software that is distributed free on a limited trial basis with the understanding that some payment will need to be made at a later date.
Payment is made by either purchasing the entire package or paying a set registration fee.
A variety of licensing restrictions are used with their copyrighted works. If you do not want the software after the trial period, it must be removed from the system. It is a prototype allowing a potential customer to sample the look and feel of the product. It is considered a type of shareware. Purchasing software under an existing site license can result in substantial savings for large numbers of users.