WP 31s is a classic RPN scientific calculator based on the powerful but more complex WP 34s. Now available on iOS too (see the support site for other emulators and for the real stuff).
It is not programmable but has a rich function set for daily use and is easier to use, thanks to a less cluttered keyboard.
A manual can be downloaded at http://sourceforge.net/projects/wp34s/files/doc/Manual_wp_31s_1_2q.pdf/download
Fixed a display bug on iPad 2 in portrait mode
Ratings and Reviews
Great replacement for the apparently orphaned HP-15C app
Was really bummed that my paid HP-15C app has not been updated in 4 years, and might not even work on the next iOS revision. But after finding this free WP-31s app, I might never need to use the old one again. The layout is simple and clean, with keyboard access to all the functions I need on a daily basis. (And menu access to plenty of functions I might or might not ever need!) A heartfelt thanks to the developers!
It's the perfect calculator I never knew existed. RPN, non-programmable (for exams), and easily accessible time calculation. Great to use on iOS, I even got it in hardware!
As a LONG TIME user of RPN (i.e. HP) calculators, this one is very familiar feeling. So far it has performed every engineer calc I've tried. I'm very impressed and pleased.
With Family Sharing set up, up to six family members can use this app.