mtCellEdit is a lightweight spreadsheet program that (Mark Tyler) created from scratch. It is a small, no frills program which is designed to handle simple day to day spreadsheet tasks. (He has) put the most important facilities ... into a small customized program which means (we) can avoid the problems of larger programs such as slow operating speeds and overcomplicated user interfaces.
Notes:
One problem with the sources was that the shared library objects do not compile as position independent code - it would be easy to fix by adding -fpic to your CFLAGS, but I just compiled with the object files directly instead... it ended up being smaller overall that way anyways.
Unlike mtpaint, there is no option to use the builtin gtk filesel, colorsel etc... - this adds ~50k to the binary (it could be reduced some just by using stock icons, but it may be worth looking at mtpaint for the gtkfilesel and gtkcolorsel code)