Erika to Satoru no Yume Bouken ("Erika and Satoru's Dream Adventure") is a fairytale-inspired menu-driven adventure game, of the sort that were very popular on the NES in Japan. The idea is to use the menu commands to interact with the world: moving around, looking around, picking up objects, talking to people, etc.
In a novel twist, the two characters of Erika and Satoru (who are depicted as twin schoolchildren) are independently playable - either a single player switches between the two, or a second player takes over the second twin. Both characters need to be in the same region to converse with NPCs, but are otherwise free to explore the map autonomously.
An odd bit of infamy related to this game is a secret developer's message that can be found if the player inputs a list of button presses after waiting some time after the game ends. Inside of which is a litany of compliments and complaints to other co-workers, including some sexual insults which are deeply at odds with the child-friendly nature of the game. It also refers to, among other things, the work Atlus did for LJN including The Karate Kid. The message and its contents are described further in this article.