Know someone who rents out property to others? Perhaps they could use a hand managing their property. If so, you can make a decent amount of money on this side business idea with relatively little work on your part (most of the time). It'll take some hustling and the willingness to be flexible with your schedule, as you'll be responsible for collecting rent checks, managing repairs and improvements, and simply being on call for emergencies. But, a property manager is essential for most real estate investors that have a large enough portfolio, so there's definitely merit to this business idea.
Research other listings in your city on AirBnB and see what the going rate is for a place like yours. You could also just rent out a private room as well or even a bed in a shared room. In fact, that's how AirBnB got its start. However, you might find it hard in the beginning without reviews, but as long as you take really good care of your guests and provide a lot of value, the reviews will eventually come rolling in.