Recently I've been to Russia and therefore decided to learn how to read the Cyrillic alphabet. After that I discovered that the Cyrillic alphabet is also used in other languages, like Belorussian or Bulgarian. That was good, because my effort to learn a new alphabet could be used to learn also other additional languages I didn't expect to. If I knew that beforehand, could be a reason to decide to learn one of those languages.
My question is: is there any (online) resource showing which language share the same (or, perhaps, similar) alphabets?