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Like Sean, I am biased towards the Mac, and I strongly recommend AppleScript as a BASIC-like language. It is versatile enough to do all manner of simple "Hello, World" apps, but it is powerful enough to allow the programmer to control other applications in extremely useful ways. In addition, AppleScript Studio allows the programmer to use AppleScript to write applications with modern GUIs.
There is plenty of information about both AppleScript and AppleScript Studio on the Apple developer site: http://developer.apple.com