This story is hilarious! It gives the history of the graphing calculator built into mac since version 8.0. Apparently, the project had been canceled, but two developers stayed on for free at apple for over six months to finish developing it. They would sneak into the building by tailgating other employees through the entrance, and hijack empty offices. Each of the two developers said he was reporting to the other one, so they were entirely autonomous.
All sorts of different employees helped them accomplish the task. In fact, the story says they probably received more aid than they would have had they been on the payroll. Eventually, their project was discovered, but by that time it was advanced enough that apple decided to include it on new macs.
Its a fascinating read! The Graphing Calculator Story