PECTUS EST QUOD DISERTUM FACIT
Our suggestions
Columns filled with numbers turned into images
ECMAScript (Javascript) library, distributed under the GPL license, that creates charts from (x)HTML tables.
Sunrise and sunset, all year long, anywhere
Graphs of sunrise/sunset and time of light for any place in the world.
Concatenate MIDI files
Perl software distributed under the GPL that does simple transformations on MIDI files.