Shareware

"Suddenly, the Shareware Demon appears! It says, 'Ahem. To the west is a horrendous chasm, which can only be passed by those who have paid their shareware fee. To find out how to perform this blessed act, select 'Shareware Info' on the title screen.' It waves and disappears in a puff of sulphurous smoke."

—Exile: Escape from the Pit

A game that can be played to a certain extent without purchasing it. If the player likes it enough to buy it, they can then play it to completion, instantly picking up exactly where they left off upon purchase without the need to install anything.

The degree to which shareware can be played prior to purchase varies:

Honorware: Some games have no limits whatsoever prior to purchase, merely relying on anything from a line of text reading “registered to: u” in the corner of the opening splash screen to increasingly strident, sometimes unskippable admonitions of shame (thus the occasional pejorative of Nagware) in order to remind receptive players to pay for the game…and the warm, fuzzy feeling of supporting independent game development.
Crippleware: One or more features are inactive until the game is purchased. This might mean that you can't exit a certain area, level up beyond a certain point, obtain certain powerups, create or use Game Mods, etc. Sometimes, features will only shut off after a trial period ends, combining this with…
Trialware: You can only play the game for a certain span of time (typically about a month,) a certain number of times, or something similar. After that, it can't be played any more until it's purchased. In the early days, this could often be circumvented by setting your system clock forward several years before installing it; on reverting to the normal time, you would be told that you are on day -3467 of your 30-day trial.

Shareware is intended to get distribution by way of players sharing it with each other via whatever means they feel like. That almost always means the internet now, but in ancient times, this took the form of telephone BBS networks, a prototype of today's Fora, or more often that of people actually copying the games onto floppies or cassettes and physically handing them to their friends (a process jokingly referred to as 'Sneaker-net' by many computer users). Since shareware games are often quite compact compared to other games, another way they would sometimes see distribution (especially once CD-ROMs caught on) was in the form of physical media sold at stores or in computer magazines for a nominal fee, which included large numbers of shareware games in much the same manner as a digest or compilation.

Buying shareware is often referred to as “registration,” because all that's usually included with one's purchase is a code (consisting of one or more special strings of letters and numbers.) This allows sales to take place via postal mail, telephone conversation, or (even over a decade before the web) online communication. When typed into the program, this code “registers” the copy installed on your machine as belonging to you and removes whatever restrictions existed in its unregistered state. This is all the Copy Protection/DRM typical shareware games have, and—most shareware authors and customers feel—all that they need.

Some games, most notably early Apogee and Id Software titles (Duke Nukem, Commander Keen, Wolfenstein 3D, Doom…) were distributed in “shareware” versions (typically only the first of three episodes), even though the full games were separate software that was physically sent to the customer by mail-order. By common terminology, such distributions are more accurately called demos (demonstrations), just usually more generously sized, such as an entire multi-stage episode rather than one or two stages. Even so, it might be argued that a certain resemblance exists between shareware and demos in some cases, such as flat subscription-based games that can segue directly from some sort of free trial to the full game, like World of Warcraft.

Arguably, the slow rise of Episodic Gaming shows a return to the concept of Shareware, at least in series which release their first episode for free.

For games that are misleading about their trial status and/or keep asking for more money even after you "buy" them, see Allegedly Free Game.

Do be aware that despite the excessive preoccupation with games above, Shareware can actually be any kind of program, and usually is.

Examples of Shareware include:

Companies and Creators

Spiderweb Software still operates on the classic shareware model, releasing 20%-40% playable versions of Nethergate and the Exile/Avernum and Geneforge series.
Ambrosia Software also operates on the shareware model for all the titles it develops and publishes, such as Escape Velocity and Aquaria.
- Escape Velocity was notable because the shareware release contained the full game plus Cap'n Hector, a friendly in-game character who would remind you to register the game. The "friendly" part only lasted until the game's trial period expired, at which point Cap'n Hector would hunt you down and murder you. And this was a game where your character could easily get Killed Off for Real.
Id Software was arguably the most famous company for using shareware. Doom only allowed the first 9 levels for free, leaving one to mail-order for the last 18 levels. Wolfenstein 3D had the same shareware model, allowing only the first 10 levels out of 50. Interestingly, Commander Keen is a special case. The first and fourth games were shareware with no limits or messages. However, the second, third and fifth installments had to be purchased, leaving parts of the story unfinished for shareware users. The sixth game had a demo of the first three levels due to a different publisher.
Nearly everything Apogee Software (aka 3D Realms) released from the late 1980s to the late 1990s had a shareware version.
Mike Sedore has "light" versions of all three of his games: Mike's Cards, Mike's Marbles and Mike's Arcade. Registering "Mike's 3-Pack" allows one to unlock all three games for the price of two.

Games and Series

Bio Menace
Blake Stone: Aliens of Gold
Blood
Bolo
Cortex Command allows you to download the game for free, but unless you pay them, you can only play for six minutes. In a weird twist, paying for the game so far doesn't actually give you the full game, per se, since the full game is still in development, but assuming they do finish it, you'll get the full game for $20 off the final price. So basically, you're paying for the chance to beta test the game. Wrap your mind around that.
- Mount and Blade had a similar set up during its development - one could download it for free, and play for one in-game month, or pay to get full access to the game as it was, and all future versions (including the completed game). The price steadily increased as the game neared completion, so the earlier in development one bought the game the cheaper it was.
Crystal Caves
Doom—Could well be the ultimate example of this trope. The shareware version offered gamers 9 levels, out of a total of 27 contained in the mail-order version (with an extra episode in the retail release, titled Ultimate Doom)… that's exactly one third of the game which was given away for free.
The Duke Nukem series -- The first three main games in the series had a complete “episode” released as shareware first, with further episodes then being available to buy.
Heretic
Immortal Defense allows you to play through the first third of the game for free, downloadable from their website.
Jazz Jackrabbit—The sequel had its own, disconnected shareware episode, made up of unique levels that could be played as its own episode in the retail version.
Jill of the Jungle
Laxius Force
Monster Bash
Quake — The original game in this series was released as shareware. It gave gamers eight levels for free, with 24 more available if you bought the full version.
- Nine if you count the Hub Level "start". Which is also a cool deathmatch level.
Real Space 3: Apocolypse Returns—Though, the three other games in the series are entirely free.
Rise of the Triad — One of first shareware releases that had an entirely different set of levels for the shareware version. All the levels included in the full release are completely new.
Secret Agent
Shadow Warrior
Traffic Department 2192
World of Goo's PC version qualifies, as it allows you to play through the entirety of its first chapter, but requires you to register the game to continue after that.
Xargon
Halloween Harry (otherwise known as Alien Carnage) is an interesting case. First it was released as Halloween Harry (with the first episode as shareware), but some thought the name would make people think it was a holiday game. So they renamed it to Alien Carnage and swapped the first and third episodes. Gamers could get the (formerly) third part for free now. That leaves only the second and fourth episodes that you had to pay for. It's all been released as freeware now, but it makes you scratch your head, doesn't it?
Mini Robot Wars
Dungeons of the Unforgiven by Moraffware. The free section contained 20 large levels and 4 bosses. Any attempt to enter a non-free area triggered a pop-up telling the player to 'phone the publisher to buy the full version (price on application).

Other Shareware

As-Easy-As, a spreadsheet designed to rival the then-dominant Lotus 1-2-3.