Teapot is a compact spreadsheet software originally written by Michael Haardt.
It features a (n)curses-based text terminal interface, and recently also a
FLTK-based GUI.

Another interesting feature is its modern approach to spread sheet theory: It
sports true three-dimensional tables and iterative expressions. And since it
breaks compatibility with the usual notions of big spreadsheet packages, it
can also throw old syntactic cruft over board which many spreadsheets still
inherit from the days of VisiCalc on ancient CP/M systems.

Optional dependency: fltk