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