From IFWiki

Shareware is a software distributing and marketing method. When an author releases a program as shareware, he or she encourages wide distribution of that program. A new user of a shareware program is entitled to evaluate it for a period set by the author. At the end of the evaluation period, if the user decides to continue using the program, he or she is asked to pay the author some amount of money. In this context, the act of paying money to the author for continued use of a shareware program is called registration. To encourage users to register, many shareware authors offer programs with more advanced features or future upgrades free or at lower cost to registered users only. Some programs also have certain features deliberately disabled or restricted in the shareware version, and these restrictions are removed when the user registers. This can be done either by sending the newly registered user a different version of the product, or by any of several unlock procedures. Obviously, while the sharing of the shareware or evaluation versions of shareware programs is allowed and encouraged, the distribution of registered versions or registration codes is not permitted.

In the context of interactive fiction, Shareware, where the author has a reasonable expectation of receiving registrations, usually works in one of a few ways. First, the author may provide only a small portion of a game for free. When a player finds the game and likes it, he registers, and the author sends the complete game to the player. The author may also distribute the complete game freely, but include one or more puzzles, the solutions to which require information distributed only to registered users. Another approach is to offer hints to registered users, or to provide the game's source code upon registration.

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