Here's another book that doesn't quite fit genres. Airborn is set in a world where the major form of long-distance air travel is drigibles and hot air balloons. The airship lift is provided by an made-up substance called hydrium and there is a sub-plot about finding a previously-undiscovered-by-civilization flying mammal. But other than that, Airborn is pretty much just a cabin-boy saves the day against pirates, shipwreck and other hardships story that could have been set on a conventional sailing ship or other long-distance conveyance. Airborn wouldn't have been written without the growing popularity of the "Steampunk" sub-genre, but it doesn't really have the full Steampunk feel.
Airborne was shelved as YA by my library, but is suitable to be given to interested middle-grade readers.