RemoveProperty[{obj, item}] removes all properties associated with item in obj.RemoveProperty[{obj, item}, name] removes the property name associated with item in obj.
RootReduce[expr] attempts to reduce expr to a single Root object.
Run
(Built-in Mathematica Symbol) Run[expr_1, expr_2, ...] generates the printed form of the expressions expr_i, separated by spaces, and runs it as an external operating system command.
ScheduledTasks[] returns a list of ScheduledTaskObject expressions that represent current tasks.
Selectable is an option for displayed objects, cells, and notebooks that specifies whether their contents can be selected interactively using the front end.
SelectionEvaluate[notebook] replaces the current selection in a notebook with the result obtained by evaluating the contents of the selection in the kernel. ...
Skeleton[n] represents a sequence of n omitted elements in an expression printed with Short or Shallow. The standard print form for Skeleton is <<n>>.
SoundVolume is an option to Sound and SoundNote and related functions that specifies the relative volume of the sound produced.
SpanCharacterRounding is an option for selections that specifies the method used for rounding a spanning character when its size is to be adjusted.
Underscript[x, y] is an object that formats as UnderscriptBox[x, y].