Stattoo is a system monitoring utility that adorns your desktop with status tattoos (hence the name), which can be used to display a wealth of information. There are a number of display panels available - known as capsules - that can display everything from the local weather forecast to the current date.
You can also used capsules to display the amount of disk space you have remaining, show your next three iCal appointments, monitor battery life and show the time. Rather than switching to your email client to check for new mail, just take a look at Stattoo which will tell you if new messages have been received.
Another useful capsule can be used to monitor web feeds which eliminates the need to launch a dedicated aggregator to keep abreast of the latest news and blog posts. It's pretty basic stuff in many respects, but it is also incredibly useful.
Individual capsules can be customised by adjusting transparency levels, size, text colour and activation hot keys. Whatever aspect of your system, or part of your online life, you would like to monitor, Stattoo enables you to d so while you get on with using your Mac.