I use several health apps, and I have a Jawbone UP24 fitness tracker that tracks my steps, and also my sleep at night. When I go to the fitness center and swim, I can also log the swimming into the app; but the band is not waterproof like an Apple Watch would be.
I have been thinking about getting a different one that also tracks heart rate as well; but I am still looking at them to find the one I want. My daughter wants to get me an Apple Watch; but I am not sure that I could learn how to work it because they are pretty complicated.
As far as health apps, I have a great little app that tracks heart rate by using the camera on my iPhone, and it also shows if my heart is out of sinus rhythm. I have one of those wrist BP monitors so I can check that when I want to, although this one does not use the phone app.
I have several of the health apps, as well as the Walgreen one that gives you Walgreens points for using it.
For my diet and food plan, I have Carb Manager, which tells me in detail the carbs, proteins, and fats in every food that I eat, as well as the vitamin and mineral content, and the fiber it has. It also has charts and graphs so I can track how well I am doing.
The reason that I use them is because(ultimately) my health is my responsibility. I am glad to have my doctor and medical information from the health clinics, as well as the medicine that I take for my heart rhythm; but I believe that it is MY responsibility to take as good of care of my body as I am able to do.
Having the right equipment and apps is a big help for me to be able to do that.