Imagine hailing a ride with your phone and having an electric plane arrive to whisk you away. That's the vision of German startup Lilium, which is developing a five-seat electric jet that can take off and land vertically, enabling it to serve some of the world's densest cities. The key is a series of engines that can rotate 90 degrees; this allows the jets to reach horizontal flying speeds of up to 186 m.p.h. (faster than many helicopters) and then descend straight down once they've reached their destination. But the jets are far from being commercially ready: Lilium only just completed its first set of test flights in Bavaria, using a two-seat prototype.
For more on these stories, visit time.com/ideas