My favourite app is available at http://www.patientslikeme.com/. This allows people to monitor their mood, weight, medication, quality of life, symptoms and side-effects etc. There are forums for mutual support for various conditions. Anonymised data is available to researchers and the information so garnered has already helped in the treatment of several conditions. It is possible to print out graphs etc to take to consultations. It would be a good cradle to grave personal health monitoring system. Caregivers including medical professionals can be invited permitting them to be kept informed of your condition. It encompasses many of the other existing apps and ideas for apps that have been mentioned here, but all in one spot, which allows interdependencies to be observed.