characters in a tile-based map. The game involves exploring dungeons which are made up of rooms and interconnecting corridors. Some games may have open areas or natural features, such as rivers, though these are considered against the Berlin Interpretation. The game presents the status of the player and the game through numbers on the game's screen/interface. Though this is not addressed by the Berlin Interpretation, roguelikes are generally single-player games. On multi-user systems, leaderboards are often shared between players. Some roguelikes allow traces of former player characters to appear in later game sessions in the form of ghosts or grave markings. Some games such as NetHack even have the player's former characters reappear as enemies within the dungeon. Multi-player turn-based derivatives such as TomeNET, MAngband, and Crossfire do exist and are playable online. Early roguelikes Early roguelikes were developed to be played on text-based user interfaces, commonly UNIX-based computer mainframes and terminals used at colleges and universities before transitioning to personal computers. Games used a mix of ASCII or ANSI characters to visually represent elements of the dungeon levels, creatures, and items on the level as in ASCII art. These games typically included one or two text lines presenting the player's current status at the bottom of the screen, and text-based menu screens to manage inventory, statistics, and other details. The player's character was nearly always represented by the @ character across text-based roguelikes, which had been chosen by the developers of Rogue to stand for "where you're at". Other common examples would include $ for monetary treasure and D for a dragon. Later games would take advantage of colour-based text graphics to increase the variation of creature types, such as a red D for a red dragon that would shoot fire, while a green D could indicate a green dragon that would shoot acid. Players would use the keyboard, using one keypress to enter a command. Sociologist Mark R. Johnson described these commonality of symbols and glyphs as semiotic codes that gave an "aesthetic construction of nostalgia" by "depicting textual symbols as aesthetic forms in their own right" and consistency across multiple roguelikes. With modern computer systems, users developed alternate means of displaying the game, such as graphical tilesets and Isometric-based graphical front ends, as well as interfaces that took advantage of keyboard and mouse UI controls, but otherwise still kept to the core tile-based gameplay. As computers offered