irisu shoukougun!
English name: Irisu Syndrome!
A free puzzle videogame starring Irisu Kyouko and her friends, Agetha, Edogawa, and Uuji, a group of university students.
Based on how you play, you will either get a Bad Ending, which leads to death of the 3 university students. Or a Good Ending where it is just a scary surprise party. Or a perfect ending (in Metsu) where Irisu becomes sane, Uuji starts down the path to sanity as well, and all 4 of them -- Irisu, Agetha, Edogawa, and Uuji are all friends.
In February 2010 an expansion called いりす症候群！滅 (Irisu syndrome! Metsu -- aka Irisu Syndrome! DESTRUCTION) was released, with hints of a 2nd expansion in the works. Though so far there are no further works from the series.