that's cool to see that the idea is supported.
I thought to share my thoughts on what I would see in a Fitness application and also tried to put some "priority" around it. But it's just my view...
I used so far
www.fitsync.com. They have applications for JAVA-mobiles and PDAs (Palm, MS, etc). It's quite a nice tool, but the JAVA app only offers to synch programs and add your training data. No changes to exercise, routines are possible, neither you can add any of the other information such as vitals or so.
Exercises (must have)
Name, Weight, Reps, Notes, nice would be a Muscle Group field as well
Routine (1)
Name
I think this would give you the basic to schedule and track a workout. You define your exercises and then group them into one or more routines, depending on your needs (e.g. split trainings, etc).
Each exercise in routine can have 1 or more sets and it would be nice to see what weight, reps you did last time
Cardio (1)
Name, Time, Distance, Notes
I believe cardio belongs to an exercise so this should also part of the program. Maybe it could just be an exercise like any other weight lifting one....
Then the nice to haves:
Vitals: height, weight, measurements of arms, legs, etc
Vitals to enable you to track how your body develops
Journal: date, notes
Just to write down how you feel, and so, but this could be just somewhere in the program or so. I would use it, as even doing the same weight and reps it still does not feel always the same and making a note for the next time would sometimes be nice.
Nutrition: What you eat and when...
I just had this idea and this is a "very nice to have", as I am following a diet to get a little of that fat of my body... Here I track what, when (they say 5 meals a day) and how many calories, carbs, proteins and fat. Beside of that, for me personally I would still want to have kind of a track, as I react to some food and sometimes I just don't remember what I ate.
But this is - I guess - a very nice to have :-)
and synching would be cool too... no that's then too much
... those my thoughts ...
I am happy to read that you will start working on a fitness app, BigBoss, but fully agree with Trent J. - a basic exercise/routine tracker to start off is way cool already.
Off for a week now to vacation... looking forward to check here what went on in that time :-)