All 118 elements of the periodic table. Cards are reverse so you'll provided either the Atomic number or Abbreviation to guess it.
Answer provides: Atomic Number, abbreviation, element name.
All elements are coloured by metal-type. Colours match the same as wikipedia:
https://en.wikipedia.org/wiki/Periodic_table
Answer provides the type of element if it's from a common group (Alkali metal, halogen, etc).
There is an extra box left blank which notes or mnemonics can be added yourself which will appear below the answer.
Tested and works on Windows and Android. Might need CSS modification in other browsers.