Lux Visual Novels • http://luxhime.wordpress.com/project-nattsu/
The protagonist is a young man, Shoichiro Yoshizumi, whose grandfather has a job as a summer remedial instruction teacher. However, his gramps' has to have a surgery, so Shoichiro will be a substitute teacher for a while... And then he discovers that he's going to teach three girls, not very far from his own age!
Release Date: May 14, 2007
Platforms: Windows, Mac OS X, Linux