Rainmeter is a desktop customization platform. Through Rainmeter, you can enhance your Windows computer at home or work with skins: handy, compact applets which float freely on your desktop, much like Windows Sidebar gagdgets, or dashboard widgets for the Mac.
A site which holds a great add-on for your computer. I have used it once or twice for long periods of time, although I have found no use for it, at least for me.
It is a completely safe website, although beware of the skins going around that are simply fakes - once you download the fakes, most likely it will contain malware, spyware, or anything of that nature. They show a warning on their website about these fake skins, which is very responsible of them. Overall, I find they are trustworthy, they offer a great add-on for free (Vendor reliability is great), privacy is average, and child safety is fine.
Rain meter is a very fun, and useful program for day to day life. It can replace windows vista/windows 7 side bar, and do anything you program it to do. It's a great foundation for if you want to do some basic logic based programming. Beginner level programming for most functions, if you want to edit existing, or create new programs.