- How fast can Usain Bolt run? A simple speed calculation with conversion.
- Cost of meetings - sometimes the only fun you can have in meetings is working out how much it is all costing.
- If an Olympic sized swimming pool was in space, how big would the sphere of water be?
- Duff's law, fun with estimating time.
- Joel Spolky's Equity Split Calculator - joelonsoftware, Fog Creek and Stack Exchange man's sage advice for splitting the equity of a startup.
- A Body Mass Index Calculator. It shouldn't be constituted as medical advice, it came from wikipedia.
- A set of constants when designing for the iPhone and iPad.
- A monthly invoice, complete with timesheets