Dungeons and Dragons:
Help/instructions are spread over 3 books, depending on the user, the player’s handbook is for the players, the Dungeon master’s guide and the monster manual are for the DM to use.
Levels are more of a concept where the players become stronger and the monsters become tougher, the DM does not have levels.
the interface is written on paper in the form of a character sheet, and as stat blocks in the books.
the content is the books used and dice to simulate chance and odds.
input/output is the players interacting with other players, the DM and the scenarios that they are in.
The rules are explicit, but can be adjusted according to the needs of the players and DM in order to have fun.