GNU Screen

GNU screen is a utility which allows the user to emulate a terminal within a terminal. While the advantage of this is not immediately apparent, screen allows the user to perform several additional tasks over a normal terminal.

Features of screen include:

1. Detatching sessions from the terminal to let them run in the background and be recovered at a later time;
2. Accessing the same session from multiple terminals (or multiple computers)
3. Running more than one session in a terminal (split-screen mode)

There are many other features - more documentation can be found in the screen (1) man page.