This is a combination of talking with Petch and an old idea we had years ago. Essentially our old idea was that we have users put their mood into their phone and their location and mood is uploaded to the internet. You could then do an overlay of google maps etc so that people can see “hot spots” where people are in a good mood (e.g. concert, cool fete etc)
The extension to this is a CBT (Cognitive Behavioral Therapy) tool which associates the mood you’re putting in a word or sentence about how you feel. The idea is that when you hit the bottom, and you have an “episode”, there is now a trail of thoughts or moods which led up to it. Then you can do some baysian analysis on it so that those words get a rating. When the user starts to go down that path again, it can warn them (maybe colour?) that the last time they were feeling like this they had an episode. No money in it, but it might help people with depression.