This game mechanic applies to games that are not story driven and can have no ending. This means that the player can play for an infinite amount of time. The game may get harder as they progress but there is no end point where the player receives a credit scene and the game ends.
This mechanic is used in a lot of mobile and flash games, a popular one being Tetris. In this game, the player has to destroy the blocks by using them to create a row. When the player destroys a row they receive points. The game does not end until the player losses at which point they receive a final score. They can then restart the game and repeat the process to try and last longer.
Another good example of this is Minecraft. Even though Minecraft technically has an ending, the game can be played for an infinite amount of hours as it is not driven by a story but by the imagination and creative mind of the player as the purpose is to build structures.
If I were to use this mechanic in my own game It would be an open world adventure. The player will be online or by themselves and have to collect resources in order to gain equipment. They can explore the world and create structures such as cities for them to live in.
This mechanic is applied mainly in MMORPG games. What this is, is items that the player receives but they can not use them because they are on the demo version of the game or a free trial. This is a good way of encouraging players to buy the game as they will be able to use the items.
Runescape is a good example of a game that uses this mechanic. The game is free to play however players can pay money every month so that they have a subscription. While they are playing in free mode they will sometime receive items from quests or even from other players such as ‘Dragon Armour’. When the player tries to equip this armour it will tell them that they need to buy a membership to be able to use this mechanic. The player is then encouraged to buy a membership which then gives the company a profit.
Another good example of this mechanic being used is in the console version of Minecraft. Players can play through a demo of the game that only lasts a certain amount of time before it will ask them to buy the game or restart the demo. Since the player has already put time into the game creating their own buildings and gathering resources they will not want to lose it. Therefore they then buy the game so that they can keep on playing.