Hvac buddy, 9.99 it does superheat subcooling and airflow (required td based on return wet and dry bulb). They also have a duct calculator app made by the same company. I believe they also recently came out with a load calculation app but I haven't tried that one yet.
I use the residential load calc ($49.99) and it's great. Easy to input data and spits out an HTML report you cn email right from the iPad to yourself and/or the customer. There's a Johnstone toolkit that helps you size cap tubes amonst other stuff,(free) a Copeland X-ref which sux most of the time but when it does find a compressor,it gives good info on it. The Tecumseh compressor app is better (both are free).
Every customer you take for granted today will be someone else's tomorrow.
My newest purchase is "Truck Stock". It takes a little set up but has really helped me with stocking and more importantly restocking my parts. also use HVAC buddy, but I have not sent a customer email with it yet. I am not sure they want one.