I’ve found this little tool invaluable. I use it to test out RegEx expressions, String Formatting and tons of other useful little bits of code.
I used to keep a dummy project around for this purpose, but it’s a pain to load VS.NET every time that you want to test a quick string formatting and it’s too painful to test to that location in your real application just to see if it worked and see what it does.
I hope that you enjoy it as much as I do.