Matched Betting (not available in the USA) enables you to gamble (nearly) risk-free. I say nearly as there is always room for error! It involves placing bets on all outcomes of an event, using free online bets given out by the Bookies. Although it may take a while to get your head around the concept, Matched Betting can make a substantial addition to your monthly income.
Like Airbnb, becoming a ridesharing driver for companies like Uber, Lyft or Sidecar is a way to join the shared economy. And though it is not technically earning money from home, it allows the same kind of flexibility and it is a way to use an asset you already own (i.e. your car) to make money. There are things to keep in mind, though, about driving other people such as whether your car insurance will cover you and how you pay taxes on your earnings.