LOL is league of Legends a DOTA copy that is free to play on PC and is proably one of the largest games on the planet right now.
http://euw.leagueoflegends.com/
The lol store is where people buy new hero skins, some people have up to 100 pounds/dollars worth of skins etc, the company has grown quite quikcly from its begining to what it is today.
Alot of game pusblishers and investors are looking at the F2P model beacuse of the sucess of riot, not all games will do as well but it looks like a good invesment option at current.