Charter, also called air taxi or ad-hoc flights require certification from the associated country's regulating body such as the FAA in the U.S. The regulations are differentiated from typical commercial/passenger service by offering a non-scheduled service. In the U.S. these flights are regulated under FAA Part 135. There are some cases where a charter operator can sell scheduled flights, but only in limited quantities.
We decided at the last minute to escape from Florida as hurricane Irma was bearing down on us, and Stratos came through for us. Despite our first choice airport running out of fuel, they managed to get some at another and we got out with about 1 hour to spare. It was a hectic time, with everyone else scrambling to escape, but Stratos made the whole experience simple and efficient for us.We will definitely fly with them another time, preferable when we're not all stressed about a hurricane aimed right at us!