[datawaslost]

Presage is great, but to clarify some other comments - it doesn't involve any specific dataset, like SwiftKey - it simply does nice smoothed predictions when given a large database of n-grams (groups of words) and their frequencies. It's fairly easy to chop up a corpus into n-grams using NLTK or other tools, and there's a good port for Python called Pressagio.

My startup Spoken - http://spokenaac.com - uses n-gram predictions to help users with aphasia or other language disorders speak. The user interface challenges aren't quite as intense as Stephen Hawking's binary input, but it's an interesting field if you're into design and big data.