SkinCalc, which is completely free, features standard and advanced calculator functionality, a spreadsheet interface, and skins. Skins make it possible to change the layout and functionality of the software, with effects that include non-rectangular shapes, user-configurable transparency and alpha channel translucency. More than 100 skins are available from the sites listed at homepage, which also has instructions to create your own skins. Calculator Functions The calculator has a variety of built-in functions which can be used to configure the user interface for custom needs. The following functions are available in the default configuration (as in the "SkinCalc" and "SkinCalc Pro" skins): Plus, Minus, Multiply, Divide, Decimal, Change Sign, Equals, Percent, Square (by pressing "Multiply Equals"), Square Root ("Divide Equals"), Memory Clear/Recall/Set/Add, Clear, Clear All ( "Clear Clear"), Backspace and drop-down menu with list of units. This configuration was designed to offer at least the full functionality of the Windows system calculator (Standard Mode). Skin files can be used to change the layout and to add/remove functionality. Additional keys that can be programmed include: Multiply and divide by Constant (very useful for adding or removing VAT), Double-Zero, Triple-Zero, Reciprocal ("1/x"), Square, Square Root, Base Conversion, Bitwise Operators, Clear All, Convert to Previously-Used Unit and Convert to Preset Unit. More advanced features include support for advertising banners, dual display, skin selection menu, button shortcuts to access the Skins tab and other software options.