I also use apps like Myfitnesspal or Lose It for clients (a great way for them to track–and if they share their food diary with me it’s great for me to review). Other than a few apps, I am also old school and like to keep files of my clients–and I use pen and paper to track. Everything is in one place and easy for me to access.
I had purchased an app called The Training Notebook and used that for a while, but it was lacking a few things (like a notes section/next appt., etc.), so I went back to taking notes by hand. They may have updated it by now, so that may be an option for you. I track my appointments with my iPhone.
Hope this helps.