Productivity tool - Twitter in Excel
mit.edu
mit.edu
:)
Excel is pretty versatile
That said, Excel is pretty capable on it's own.
I built an entire timesheet data collection system for a large organisation in 2000 using Excel+VBA in Office 2000. It wrote data in CSV format onto a network share which was pumped into their AS400. It scaled quite happily across 45000 (!) global users...
Thinking back, it is astonishing all the things one can jury rig together- from plain Jane spreadsheets to an interview candidate tracking & scheduling system to Japanese candlestick charting