NumberSeparator is an option for NumberForm and related functions which gives the string to insert at breaks between digits.
OpenAppend["file"] opens a file to append output to it, and returns an OutputStream object.
RootApproximant[x] converts the number x to one of the "simplest" algebraic numbers that approximates it well.RootApproximant[x, n] finds an algebraic number of degree at ...
SectorOrigin is an option to PieChart and related functions that specifies where sectors should start.
SelfLoopStyle is an option for GraphPlot and related functions that specifies how to draw self-loops that connect a vertex to itself.
SignificanceLevel is an option to VarianceTest and similar functions that controls cutoffs for diagnostic tests as well as test conclusions.
SimilarityRules is an option for functions such as SequenceAlignment that gives a list of rules for similarity scores to assume between pairs of elements.
VertexLabeling is an option for GraphPlot and related functions which specifies whether labeling should be included by default for vertices in graphs.
VertexLabelStyle is an option and property for Graph and related functions that specifies the style to use for vertex labels.
ViewAngle is an option for Graphics3D and related functions which gives the opening half-angle for a simulated camera used to view the three-dimensional scene.