DateString — current or specified date as a string in many possible formats
$DateStringFormat — default date string format
$TimeZone — resettable current time zone
DateList — date elements as numbers in

format
Clock — real-time dynamic clock variable
DatePlus — add or subtract days, weeks, etc. to a date list or string
DateDifference — find the difference in days, weeks, etc. between two dates
DateListPlot,
DateListLogPlot — plot data associated with dates in any format
DatePattern — date pattern for string manipulation