GNU screen

Or, what sort of things you can do with screen and the commands that control them.

• Multiuser - Allowing multiple users on a system to interact with a single screen instance.
• Monitoring - Letting screen monitor your windows for interesting behavior.
• Terminal - How screen interacts with terminals, and how programs interact with screen's virtual terminal.
• Appearance - Controlling how screen looks and communicates with the user.
• Interface - Controlling how the user communicates with screen.
• Text Exchange - How screen can facilitate text exchange among programs, files, and screen itself.
• Window Management - Managing windows in screen.
• Region Management - Managing regions in the display.
• Misc - Everything else.