tmux is a terminal multiplexer
What is a terminal multiplexer? It lets you switch easily between several programs in one terminal, detach them (they keep running in the background) and reattach them to a different terminal. And do a lot more. See the manual.
Download tmux %%VERSION%% or get the development version.
tmux is hosted on SourceForge and needs libevent and ncurses .
There are some programs to use with tmux on GitHub and a book on tmux.