Gym Buddy is an essential workout application. Not only does it allow you to focus on certain groups of muscles, but it helps you get the most out of your workouts. While resting one muscle, you're building another. Don't know how much weight you should be lifting? There's a benchmark utility for that! Plug in your basic benchmark values and it will give you starting values for weight lifting. These aren't exact values, but will set you off in the right direction.
Choose from Upperbody, Lowerbody, or Core; and then choose sub-workouts to focus on specific muscles within these areas.
There will no longer be a pro version! This will be a 100% free application, and all the pro version features will be slowly added into the current version.