Model railroading is a graying hobby full of collectors who never learned to buy online. One operator built a multi-million-dollar store by being the person who did. You don't have to love the hobby, just out-market the incumbents.

Most people think farming means land. One grower did more than $150,000 a year out of a room the size of a parking space, selling greens by the tray to restaurants that reorder every week. Here's why revenue per square foot beats acreage.

A commercial airline pilot bought a five-acre worm farm and turned dairy manure into soil that sells for hundreds of dollars a cubic yard. His customers are Napa vineyards. The feedstock is often free.