Free-to-play
Free-to-play (F2P) refers to any videogame that has an option of allowing its players to play without paying. Some of these games have both a free version and a Pay-to-play version that offers the full version of the game and all of the updates. Popular MMORPG example are Rappelz, Flyff, GunZ, GunBound, RuneScape, Space Cowboy Online, MapleStory, and Conquer Online. Of course there are other games that are Free-to-play.
Many game developers keep a free-to-play version running so people can try out their game before paying the membership costs. It also helps in that the game may receive higher ratings, attracting more people to it. Other developers, for example softnyx, generate revenue by selling in-game items that significantly enhance the player's in-game experience.
There are also many website provide free online Flash games, e.g. F2P.org
The term free-forever game is used to distinguish MMORPGs that promise to never charge a monthly fee from those that are currently free-to-play but may become pay-to-play in the future. It applies only to MMORPGs because while a conventional freeware game becomes free-forever as soon as it it is downloaded into a player's hard drive, a free MMORPG may start charging a fee and instantly transform into a pay-to-play game.