Played all three of the original NDS games, and thought, "man, it would be the coolest thing ever to have this on PC where you could make your own songs for it!" So I googled something like "Elite Beat Agents/Osu Tatakae Ouendan fan game", and was so surprised and happy to see there actually WAS something exactly along the lines of what I was looking for! That was YEARS ago, and it's still one of my favorite games to date (Whenever my friends see me playing, they tend to be speechless, then they say, "You're... REALLY good." xD)!
EDIT: Little do they know about people like cookiezi and rrtyui. xD