A little known novel type game, comes in a hentai version (with badly written hentai scenes) and a child friendly version. Only in japanese, though 57% has been put into a translation patch.
Also has anime
of it, as well as an epilogue. And some spin off games and manga.
Made by Key
Hey, I just brought that Kanon game off the web! It's supposed to actually be a good game that focuses on the story and not the main character's breasts!