Human Calculator 

Compact and helpful calculator for windows. General features: 1) 40 built-in functions 2) Syntax highlight of math expressions 3) Clipboard smart functionality 4) Four numerical systems for entering and printing numbers
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SkinCalc 

SkinCalc is a free calculator featuring skins and a spreadsheet interface. Skin effects include translucency and non-rectangular shapes. More than 100 skins are available from the sites listed at skincalc.com.
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