In 1996, at the time of the game's release, Internet-based gaming was just beginning and "Duke Nukem 3D" could be played on IPX LAN or modem. "Duke Nukem 3D" players often used the IPX network utility Kali or the Total Entertainment Network (TEN) online service. Kali allowed users to join a chat room to find opponents. The Total Entertainment Network had hundreds of Duke 3D players online at any time, but players had to pay money monthly for it. The game's levels are often used as the battlegrounds for these online players, bur users are able to create their own levels ("maps"). The game also features co-operative play (co-op) which allows players to fight against the aliens instead of each other. In the "Atomic" version, a new game play mode was introduced: Duke Tag, a "capture the flag" style mode.