(Vit)ality is a plugin that makes (V)im play nicely with (i)Term 2 and (t)mux.
Vitality restores the FocusLost and FocusGained autocommand functionality.
Now Vim can save when iTerm 2 loses focus, even if it's inside tmux!
It also handles switching the cursor to a bar shaped one when in insert mode, and restoring it when not.
Pull requests for other helpful behavior are welcome.
Use Pathogen to install.
You shouldn't need to do anything else, but you can read :help vitality if
you're curious.
If you find that FocusLost events are not working in later versions of tmux
try adding the following line to your .tmux.conf.
set -g focus-events on
Don't forget to restart all your tmux sessions for this setting to take effect (or just run the command in tmux itself to avoid having to restart).
MIT/X11