Before there were smartphones, there were personal digital assistants like the Palm Pilot, Handspring Visor, and Compaq/HP iPAQ line of devices. And before those, there were really basic PDAs, like ...

So you've already outgrown Arduino's most beginner-friendly board, the Uno, and are looking to move on to bigger, more exciting projects. In that case, the Nano family might just be what you need.