League of Legends
League of Legends is a free to play online video game created by Riot Games. It was inspired by a user created Warcraft 3 mod called Defense of the Ancients, or DotA. It is, as of 2013, the most played video game in the world with over 32 million active users per month. 
In League of Legends players can control 1 of 114 'champions' and team up with either one to four other players to fight another team of the same size. The two teams fight to destroy each others base structure, called a Nexus. The map is split into three lanes with three turrets and an inhibitor on each. Players must destroy each turret in any particular lane before they can attack the Nexus. The Nexus also spawns AI controlled minions for each team, who move forward and attack the first enemy champion or turret they see. These minions, and enemy players, can be killed by the players to gain gold which can be spent on items to further improve their champion.
Between each lane are paths where neutral monsters spawn, called the jungle. Either side can kill these monsters to gain gold, experience and buffs.
Each champion has three normal abilities and an ultimate ability. Killing minions, jungle monsters and enemy champions gives experience and when a certain amount is reached the champion 'levels up' and the player can spend a point to improve one of their abilities. Their are 18 levels and points can be spent in any order, except on ultimate abilities which are only unlocked for improvement at levels 6, 11 and 16.