IProfessor Laurance Kotlikoff of Boston University has wide-ranging interests, studying a number of topics over the years, especially fiscal policy. He's also head of Economic Security Planning, inc, which has a detailed personal finance software package, ESPlanner. The personal finance tool developed by a group of economists is highly influenced by economic theory. No surprise there.

In essence, economists believe in the concept of life-cycle smoothing. The idea is to figure out the highest possible standard of living you can maintain over a lifetime. For instance, with this kind of approach savings isn't an end in itself. What matters is spending, and saving is important as it helps smooth out your living standard over time. "To economists, spending is the main event, not an afterthought," wrote Peter Coy of Business Week in an early review of the product.

The firm has now come out with a simplified, free online version. It's worth checking out at www.esplanner.com/basic.

Follow Chris Farrell at @cfarrellecon