Most use the Arabic system... i.e. 1,2,3 etc. This is known as the decimal, or to base ten, system, and there are many others: binary, quaternaty, octal, hexadecimal - all of which use some or all of the numbers 1,2,3,4,5,6,7,8,9,0 and A,B,C,D,E,F.
Then there is Roman numerals: I,V,X,L,C,D,M.
There are also others on wikipedia - take a browse!
https://en.wikipedia.org/wiki/Numeral_system