Tmux Improving the console - ProgrammingAce/RecommendedLearning GitHub Wiki
Getting Started with tmux
tmux is a Terminal Multiplexer (which is what the application is named after). It has a couple of important features. It lets you split your terminal into multiple, independent shells, and it acts as a server so that your sessions keep running even if your terminal is disconnected.
Neither of these sound groundbreaking, but the combination lets you do some cool things. Seeing as how tmux is a server application, multiple people can connect to the same session and share a terminal; it's a great tool for pairing. But you can take that usability even further when each person is sharing terminal output while independently editing the source code in a single file, while being able to see what the other person is working on.