There’s an online sharing marketplace for everything these days. The latest vertical to pop up on our radar: private flights.

Boston startup Flytenow is working to do just that, and startup incubator Y Combinator is putting its money behind it as part of its current batch of startups.

The problem for folks who have a private pilot’s license is that flying alone can be expensive (both owning and renting a plane, as well as fuel costs). At the same time, lots of non-pilots would love to take some flights, either for fun or to get from one place to another.

To help both groups — pilots and would-be passengers — Flytenow has built a flight-booking site on which pilots post the trips, called “adventures,” they’re planning to take. They open these trips up to others might be interested in coming along and splitting the costs with them. It’s like posting on Facebook that you’re planning to drive to Los Angeles from San Francisco for a weekend getaway, and a friend or two asking to join and pitch in for gas and snacks money.