One of the standard accessories in Windows Mobile – Calculator – was left out from customization by HTC. Yes, it’s the same; some might even call it “ugly” looking application that hasn’t changed a bit over the years.
XDA Developers offer what they call The REAL Diamond-style Calculator. It is Multilanguage – available in English and 6 other languages, and it is available from its home thread in the shape of different cab files for different languages. After you install it to Device, you will get a calculator that will follow the general aspect of the HTC Touch Diamond/Raphael interface, so if you really “hate” the stock calculator aspect and you have a Diamond or a Raphael, this one is for you.