Well, you probably say "Heck, another MUI-based calculator",
but just check it out :

MUIProCalc is a MUI-based calculator much like Jimmy Yang`s
Calc 3.0. It still lacks the plotter, but it offers a quite
flexible history facility for inserting previously entered
expressions. Different output formats offered and plenty of
functions the user may choose from. Furthermore the look
of the calculator may be customized. ARexx Port for ease of
calculating from within an editor. Some functions are able to
return TeX compatible output. Results or inputs may be copied
to the Clipboard.


Changes to version 1.5

     - Recompilded using SAS-C 6.56 and MUI 3.0 header

     - MCalc didn`t calc the (n over k) function correctly. It used
       to calculate n!/(n-k)!, not n!/(k! * (n-k)!)
       (Reported by :Andreas Gabold)

     - Archive didn`t contain Protos.h header file
       (Reported by : Kay-Uwe Drankmeister)

     - Function group was vertically sizable. Changed
       (Reported by : Kay-Uwe Drankmeister)

     - Within the Prefs window, some entries positions in the cycle
       chain were mixed up.
       (Reported by : Kay-Uwe Drankmeister)

     - RegisterGroup wasn`t contained in CycleChain
       (Reported by : Kay-Uwe Drankmeister)

     - LinReg, StdDev, and Constants windows won`t have menus
       anymore, sorry ;)

     - Std.Deviation, Lin.Regression and Constants window didn`t
       have a cycle-chain set.
       (Reported by : Kay-Uwe Drankmeister)

     - Changed items within "Windows" menu, to toggle menus

 PERMSSN    UID  GID    PACKED    SIZE  RATIO     CRC       STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                  591    1233  47.9% -lh5- fe7a Jan 21  1995 MCalc.info
[generic]                  935    1725  54.2% -lh5- 06ba Nov 29  1995 MCalc/.Product-Info
[generic]                  700    1542  45.4% -lh5- 2014 Nov 29  1995 MCalc/ARexx/Calc.ced
[generic]                  701    1545  45.4% -lh5- 9173 Nov 29  1995 MCalc/ARexx/CalcTeX.ced
[generic]                29149   69016  42.2% -lh5- 25de Nov 29  1995 MCalc/MCalc
[generic]                10640   33641  31.6% -lh5- 5621 Nov 29  1995 MCalc/MCalc.doc
[generic]                  207     459  45.1% -lh5- 09e5 Nov 29  1995 MCalc/MCalc.doc.info
[generic]                12574   41571  30.2% -lh5- 4b94 Nov 29  1995 MCalc/MCalc.guide
[generic]                  219     465  47.1% -lh5- 6bff Nov 29  1995 MCalc/MCalc.guide.info
[generic]                  970    1601  60.6% -lh5- 63b1 Nov 29  1995 MCalc/MCalc.info
[generic]                15841   97698  16.2% -lh5- ac4c Nov 29  1995 MCalc/Source/MCalc.c
[generic]                 4637   17446  26.6% -lh5- fc1a Nov 29  1995 MCalc/Source/MCalc.h
[generic]                12532   41193  30.4% -lh5- 89a1 Nov 29  1995 MCalc/Source/MCalc.texinfo
[generic]                  513    1398  36.7% -lh5- 9669 Nov 29  1995 MCalc/Source/MCalc_gst.c
[generic]                 3296   20300  16.2% -lh5- df88 Nov 29  1995 MCalc/Source/MCalcARexx.c
[generic]                  864    3833  22.5% -lh5- 617f Nov 29  1995 MCalc/Source/MCalcASM.Asm
[generic]                 3795   21035  18.0% -lh5- cf7a Nov 29  1995 MCalc/Source/Parser.y
[generic]                  178     327  54.4% -lh5- 7e65 Nov 29  1995 MCalc/Source/Protos.h
[generic]                 2237   10622  21.1% -lh5- cdfd Nov 29  1995 MCalc/Source/Scanner.l
[generic]                  215     336  64.0% -lh5- e685 Nov 29  1995 MCalc/Source/SCOPTIONS
[generic]                  502     950  52.8% -lh5- 57f6 Nov 29  1995 MCalc/Source/SMakeFile
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total        21 files  101296  367936  27.5%            Dec 10  1995