I have used screen since the 90s and these are the features along with being able to use screen key bindings (ctrl-a as the PREFIX) is what made me switch to tmux. Please look at the tutorial at the top of my .tmux.conf file to see a few more things it can do. screen may also have these same features, but I wanted to learn tmux anyway because it seems to be more popular now.

Feature 1

You can split one window into multiple panes. These can be either horizontal or vertical. If you press prefix " to create two horizontal panes, there will be a line to divide them. You can then click on that line to resize the panes (making one larger while the other one becomes smaller). This even works in Putty and iTerm2.

Feature 2

Two people can attach to the same session. I could see this being useful in a training or troubleshooting scenario.

tmux.conf