From the tmux website:
tmux is a terminal multiplexer: it enables a number of terminals (or windows), each running a separate program, to be created, accessed, and controlled from a single screen. tmux may be detached from a screen and continue running in the background, then later reattached.
- Runs on OpenBSD, FreeBSD, NetBSD, Linux and OS X
- Panes - similar to the ones found in Vim
- Client-Server model, allowing windows to be moved across sessions and allowing multiple clients to share the same session
- 256-color support
- UTF-8 support