Shareware: a business model sorted by release date

Shareware is a type of software distribution model that allows users to try a program before purchasing it. It's a marketing strategy and distribution method that was particularly popular in the early days of personal computing, primarily during the 1980s and 1990s.
Shareware games were released for free with limited functionality (for example: no saving, missing levels, time limit), often via a BBS (Bulletin Board System), a floppy disc or a CD included in a printed magazine or by direct download (when internet was in its infancy). If the user liked the shareware product, they could pay to obtain an upgrade and unlock the full game. When digital distribution started to become popular, shareware games slowly faded into oblivion.

Most popular shareware games

Quake

shooterDOS, Windows XP/98/95

Jill of the Jungle

actionDOS

Commander Keen 1: Marooned on Mars

actionDOS