As shown in Section 6, in the top 100 apps in the Medical category, medical information reference apps numbered the most. However, within the 14 five-star ones among those top 100 apps, tracking tools numbered the most. It was obviously that as desktop e-health applications were ported to mobile devices, user preference changed. Medical information references may be convenient to use while a user is near a computer, but tracking tools are more convenient to use when they are deployed on a mobile device that stays with the user all the time. So, there is great potential for mhealth applications that can take advantage of unique smart phone features such as context awareness (including location awareness, preference-awareness, and network-awareness) and 24 × 7 accessibility.