DefaultFrameTicksStyle is a low-level option for 2D graphics functions that specifies the default style to use in rendering frame ticks.
DefaultGridLinesStyle is a low-level option for 2D graphics functions that specifies the default style to use in rendering grid lines.
DefaultMenuStyle is a low-level option for menu-generating constructs that specifies the default style to use for displaying menu items.
Deletable is an option for Cell that specifies whether the cell can be deleted interactively using the front end.
DifferentialD[x] displays as \[DifferentialD]x.
Environment["var"] gives the value of an operating system environment variable.
FieldHint is an option for InputField that specifies contents to display when the input field is empty.
FindGeoLocation[] attempts to find the current geodetic location of your computer.
FrontEndDynamicExpression is a global front end option that specifies an expression to be dynamically updated whenever the front end is running.
GeneratedCell is an option for Cell that indicates whether the cell was generated from the kernel.