We code for iPhones/iPads (iOS), that can be sold on iTunes.
We also code for Android, which can be sold on Google Play and Amazon Appstore.
Generally we code and finalise iOS first, as having iOS code can significantly speed up Android coding (the reverse is not true).
We can code for Windows Phone but recommend you evaluate the financial viability of smaller platforms first.
We also code for web apps that can be used by any browser on any platform.
Our Data-vault uses MySQL.