For this reason, MUDs are frequently referred to as text-based virtual realities.
MUDs generally have many users connected at the same time.
All of those users are browsing and manipulating the same database and can encounter both the other users and their newly-created objects. MUD users can also communicate with each other directly, in real time, usually by typing messages that are seen by all other users in the same room. Visual - use graphics, icons, visual tools, identification of users etc. Most interaction will be asynchronous. Tool A CAL program which assists learning but which itself has little knowledge content.