In-game items can be purely cosmetic, enhance the power of the player, accelerate progression speed, and many more. A common technique used by developers of these games is for the items purchased to have a time limit; after this expires, the item must be repurchased before the user can continue. Another commonly seen mechanic is the use of two in-game currencies: one earned through normal gameplay, and another which can be purchased with real-world money. The second, "premium" currency is sometimes given out in small amounts to non-paying players at certain times, such as when they first start the game, complete a quest, or refer a friend to the game. Many browser games have an "energy bar" that depletes when the player takes actions. These games then sell items such as coffee or snacks to refill the bar.
