tmux (the terminal multiplexer)
On my Linux systems, I’ll open as many as six different terminals across a trio of monitors. These are beautifully arranged automatically for me by the dwm window manager (Update: I’ve also been experimenting with awesome wm).
As I continue to SSH into remote computers for both home and work use, I’m finding myself hampered by the need to re-connect via SSH for every single terminal I open. (Update: Well, yes and no on the "hampered". Opening separate virtual terminal windows has its advantages…)
If you’ve got a flaky connection or an ongoing project, it’s really nice to be able to keep a session alive that is in exactly the state where you left it when you reconnect!
I’ve been happy with my tmux usage. I’m not doing very many super advanced things, but I’m comfortable with the basics.