Here is a little bit to get started. I'm sure others will chime in with more.
Strelok, ballistic software.
Ballistics, ballistic software.
BrassBadger ammo tracker. Ammunition in stock tracker for large retail stores.
Shot preparation related:
Maps Ruler, map distance app which is useful for getting distance between two points. Can also used for other orienteering purposes.
Smart Measure, a range finder application that estimate range based on the dimensions of distant object. useful when you don't know the exact location of your target.
Not shooting related, but useful (converting European load data in grams to Imperial grains for example).
Converter, switches between metric and imperial and other units of measure.
Hope this helps,
Jimro