Steampunk

 Etiquette & Espionage, by Gail Carriger:  In an alternate England of 1851, spirited fourteen-year-old Sophronia is enrolled in a finishing school where, she is suprised to learn, lessons include not only the fine arts of dance, dress, and etiquette, but also diversion, deceit, and espionage.

 Airman, by Eoin Colfer: In the late nineteenth century, when Conor Broekhart discovers a conspiracy to overthrow the king, he is branded a traitor, imprisoned, and forced to mine for diamonds under brutal conditions while he plans a daring escape from Little Saltee prison by way of a flying machine that he must design, build, and, hardest of all, trust to carry him to safety.

 Cinder, by Marissa Meyer: As plague ravages the overcrowded Earth, observed by a ruthless lunar people, Cinder, a gifted mechanic and cyborg, becomes involved with handsome Prince Kai and must uncover secrets about her past in order to protect the world in this futuristic Cinderella story.

 Airborn, by Kenneth Oppel: Matt, a young cabin boy aboard an airship, and Kate, a wealthy young girl traveling with her chaperone, team up to search for the existence of mysterious winged creatures reportedly living hundreds of feet above the Earth's surface.

 The Golden Compass, by Philip Pullman: Accompanied by her daemon, Lyra Belacqua sets out to prevent her best friend and other kidnapped children from becoming the subject of gruesome experiments in the Far North.

 Fever Crumb (trilogy), by Philip Reeve: Foundling Fever Crumb has been raised as an engineer although females in the future London  are not believed capable of rational thought, but at fourteen she leaves her sheltered world and begins to learn truths about her past while facing danger in the present.

 Mortal Engines (series), by Philip Reeve: Larklight, by Philip Reeve: In an alternate Victorian England, young Arthur and his sister Myrtle, residents of Larklight, a floating house in one of Her Majesty's outer space territories, uncover a spidery plot to destroy the solar system.

 Incarceron, by Catherine Fisher: To free herself from an upcoming arranged marriage, Claudia, the daughter of the Warden of Incarceron, a futuristic prison with a mind of its own, decides to help a young prisoner escape.

 Peculiars, by Maureen McQuerry: Eighteen-year-old Lena Mattacascar sets out for Scree, a weird place inhabited by Peculiars, seeking the father who left when she was young, but on the way she meets young librarian Jimson Quiggley and handsome marshall Thomas Saltre, who complicate her plans.

 Leviathan (trilogy), by Scott Westerfeld: In an alternate 1914 Europe, fifteen-year-old Austrian Prince Alek, on the run from the Clanker Powers who are attempting to take over the globe using mechanical machinery, forms an uneasy alliance with Deryn who, disguised as a boy to join the British Air Service, is learning to fly genetically-engineered beasts.