rca is simple, yet extremely versatile:

• It's a reverse polish notation calculator in the HP tradition.

      34 11 *
                                   374
      sto
      52 13 /
                                     4
      rcl
                                   374
      *
                                 1,496
  

• It seamlessly evaluates infix-style expressions, either mixed with RPN input, or in a full-time infix mode (not shown here).

      ((lastx + pi) * 2)
                                 2,998.28
      3 /
                                   999.428
  

• It runs in either floating point or integer mode.

      D
       Mode is signed decimal (D).  Integer math with 64 bits.
                                   374
                                 1,496
                                   999     # warning: accuracy lost, was 999.4277284357265288
  

• It has the trig and math functions of a scientific calculator.

      30 sin 2 ^ 30 cos 2 ^ + sqrt
                                     1.000
  

  or

      (sqrt (sin(30) ** 2 + cos(30) ** 2))
                                     1.000
  

• It has the word width selection, bitwise operators, and multiple bases of a programmer's calculator.

      32 bits H
       Mode is hex (H).  Integer math with 32 bits.
      1 zerofill
       Zero fill of hex/octal/binary output is now on
      5
                           0x0000,0005
      8 rol
                           0x0000,0500
      0x80010000 |
                           0x8001,0500
      b
                                0b10000000,00000001,00000101,00000000
  

• It supports variables.

      (_a = 7 + 10; _b = 11 + 43)
                                    54
      (_sum = _a + _b)
                                    71
      variables
                         _a  17
                         _b  54
                       _sum  71
  

• It can be trivially incorporated into shell scripts.

      $ source rca_float
      $ foo=$(fe "22 / 7")
      $ echo $foo
      3.143
      $ fc "$foo > 3.1" && echo yes
      yes
  

• rca is written in C, uses the native floating point library, and is maintained in a single source file. It's not an an arbitrary precision calculator like dc or bc: it's a convenient, non-programmable, desktop calculator, for typical one-off professional and everyday problems.

The man page and rca's help text have all the details.

rca is hosted at github.

The license can be found in the source or viewed with rca's "license" command. (It's BSD-2-Clause.)