Fangames are video games made by fans based on one or more established video games; the vast majority of fangames that have been successfully completed and published are adventure games. Many fangames attempt to clone the original game's design, gameplay and characters, but it is equally common for fans to develop a unique game using another only as a template. Fangames are either developed as standalone games with their own engines, or as modifications to existing games that "piggyback" on the other's engines.