Caffeine
Caffeine. If you have a laptop and take it to meetings or use it to give conference presentations, this is an invaluable tool. You can keep your default screen saver and sleep settings for conserving battery while mobile, but override them when you don’t want to be interrupted.
“Caffeine is a tiny program that puts an icon in the right side of your menu bar. Click it to prevent your Mac from automatically going to sleep, dimming the screen or starting screen savers. Click it again to go back. Right-click (or ⌘-click) the icon to show the menu.”
(Part of the mini-series: a miscellany of tools and software for the Mac.)
