To commemorate the declaration of World War I, the Raspberry Pi Foundation has released an educational resource in which you can build your very own morse code machine. The Pi can even interpret the morse signals and tell you what has been sent. This is a great project, especially over the summer holiday. See this new resource here.
A lot of complicated mathematics goes into any quadcopter project and normally it's left to real-time devices like Arduinos. This quadcopter, however, is driven by a Raspberry Pi. It runs a piece of software called PenguPilot and you can see a flight demo video below. More details on the project can be found here.
Model Train Set
[youtube http://www.youtube.com/watch?v=04Icexj0m1w&w=400] Jonathan Porta has written a client/server application using Node.js and Angular.js on the Pi to control a model train set. He strapped a GoPro to the roof of the train and has got some great footage (below). You can view the code here and you can expect a write-up on his blog in the near future.