cal

Display a calendar

Syntax
      cal [-mjy] [[month] year]

Options:

     -m      Display monday as the first day of the week.

     -j      Display julian dates (days one-based, numbered from January 1).

     -y      Display a calendar for the current year.

    A single parameter specifies the 4 digit year (1 - 9999) to be displayed.

    Two parameters denote the Month (1 - 12) and Year (1 - 9999).

    If arguments are not specified, the current month is displayed.

    A year starts on 01 Jan.

"If everything seems under control, then you're not going fast enough" ~ Mario Andretti

Related linux commands:

dc - Desk Calculator.
factor - Print prime factors.
units - Convert units from one scale to another.
wc - Print byte, word, and line counts.
Calculate the day of the week, for any date, in your head.
Equivalent Windows command: SET /A command does basic arithmetic.