My latest app, Diving Buddy, recently hit the iOS app store. The app contains a bunch of reference material, diving tips, and calculators for divers of all skill levels.
The app is capable of calculating oxygen toxicity levels over multiple dives, the minimum gas required for an ascent from any depth, the overall run time of a dive, the maximum operating depth, the weight of air in a cylinder so you can determine how much weight to add or remove, and various other calculators.
Each calculator is capable of displaying units in Imperial or Metric. You can even choose to have Imperial for one unit and Metric for another, since divers around the world tend to mix and match!
The diver can set his/her default values for breathing rate, cylinder size, cylinder pressure, and body weight. These values are then automatically inserted when the user adds a new calculation.
There are diving tips for how to lead a dive, how to dive safely, understanding nitrox, diving before/after flying, diving after altitude changes, and diving as a three. Each of which has been written by master divers with decades of experience.
From a technical perspective, Diving Buddy is compatible with both iOS 6 and 7. The designs and coding was all done by myself. It is performant - I wanted a low memory footprint.
There is still so much more to add to Diving Buddy, and I will continue to support it so long as interest is there. I truly believe it is something worth having for any diver.