I built this quickly using MIT Appinventor to suit my needs: I just moved to Dubai and wanted a simple way to convert from dirhams (AED) to euros (EUR) and vice-versa.
Jus enter a quantity in AED and push the "Convert to EUR" button, or enter a quantity in EUR and push the "convert to AED" button.
I did not have a mobile data plan so I could not use other apps that are free but show ads. For the same reason, the app does not check the exchange rate on the internet (but allows you to change it).
The app allows you to change the exchange rate.
The app contains a look-up table to know the most common conversions at a glance.