In general, an abacus is a mechanical calculating tool, up to today used in Russia, Japan, Korea and China. See TkSoroban for an emulation of the Japanese kind.
Abacus is a Tcl/Tk/C++/C spreadsheet developed for Linux. It supports graphics, printing, saving and loading different formats, cell editing, sorting, column and row manipulation, cell formats, undo/redo, formulas, and more.
The programming team (in Portugal) also references a tool called Abacus for the Palm Pilot; however I don't believe it has any Tcl/Tk connection.
josh: It would be fun to be able to play around with an exe Windows version of this program, compiled in this manner: See How to compile a TCL script into an EXE program.
In fact this program is really complete. It has all sorts of spreadsheet functions built into it. The Portugal Tcl-Tk connection did really fine precision work!
However, I for one would be pretty happy to simply be able to create small unpretentious spreadsheets; I won't need all the sophistication Abacus has. Therefore a small -call it- Mini Abacus stripped of many functions and holding in a meg or so would do the job perfectly for me and I believe for many of us.