For old nerds like me, only RPN calculators will do! The landscape mode of this application is particularly nice, because it makes your N900 into something close to an old HP 10C series calculator (but better). The layout and form-factor of the 10C series was just about perfect.

This application installs an icon in a wrong place (typo?). It uses /usr/share/icons/hicolor/scaleable/hildon/, which should be "scalable".