This is about the Slavic languages only – I’ll reserve comment on other languages written in Cyrillic until it becomes a live issue for me.

Everyone always starts with Russian, purely because it has the most speakers of the six Slavic languages written in Cyrillic. I will take it the other way round, and start with Macedonian, my favourite in any case.

Macedonian alphabet: А Б В Г Д Ѓ Е Ж З Ѕ И Ј К Л Љ М Н Њ О П Р С Т Ќ У Ф Х Ц Ч Џ Ш and а б в г д ѓ е ж з ѕ и ј к л љ м н њ о п р с т ќ у ф х ц ч џ ш – 31 letters, of which Ѓѓ Ѕѕ and Ќќ are used only in Macedonian, and Јј Љљ Њњ and Џџ are used also in Serbian but not in the other Cyrillic Slavic alphabets. Ѓѓ is not far from Serbian Ђђ, and Ќќ similarly close to Serbian Ћћ.

Serbian alphabet: А Б В Г Д Ђ Е Ж З И Ј К Л Љ М Н Њ О П Р С Т Ћ У Ф Х Ц Ч Џ Ш and а б в г д ђ е ж з и ј к л љ м н њ о п р с т ћ у ф х ц ч џ ш – 30 letters, similar to Macedonian, but there is no Ѕѕ, and Ђђ and Ћћ replace Ѓѓ and Ќќ, even to the point of being in the same place in alphabetical order.

Bulgarian alphabet: А Б В Г Д Е Ж З И Й К Л М Н О П Р С Т У Ф Х Ц Ч Ш Щ Ъ Ь Ю Я and а б в г д е ж з и й к л м н о п р с т у ф х ц ч ш щ ъ ь ю я – Like Serbian, has 30 letters, but with six differences. Bulgarian is linguistically very close to Macedonian, but orthographically more inspired by the eatern tradition around Russian. So instead of palatalization going on the preceding consonants, as in Serbian Ђђ Љљ Њњ and Ћћ, it is put on the next vowel, as in Юю and Яя, or Ьь (before Оо). The role of the Serbian semivowel Јј after vowels is taken by Йй. There is no Џџ. Щщ is shared with Ukrainian and Russian and Ъъ with Russian only, but both are pronounced quite differently in Bulgarian.

Belarusian alphabet: А Б В Г Д Е Ё Ж З І Й К Л М Н О П Р С Т У Ў Ф Х Ц Ч Ш Ы Ь Э Ю Я and а б в г д е ё ж з і й к л м н о п р с т у ў ф х ц ч ш ы ь э ю я – 32 letters. Іі replaces Ии as used in all others (except Ukrainian which has both). Ўў is unique to Belarusian. Ёё Ыы and Ээ are used in only Belarusian and Russian. No Ъъ or Щщ.

Ukrainian alphabet: А Б В Г Ґ Д Е Є Ж З И І Ї Й К Л М Н О П Р С Т У Ф Х Ц Ч Ш Щ Ь Ю Я and а б в г ґ д е є ж з и і ї й к л м н о п р с т у ф х ц ч ш щ ь ю я – 33 letters, this really is a case of throwing in everything you can find. Ґґ Єє and ЇЇ are unique to Ukrainian; Іі is shared only with Belarusian.

Russian alphabet: А Б В Г Д Е Ё Ж З И Й К Л М Н О П Р С Т У Ф Х Ц Ч Ш Щ Ъ Ы Ь Э Ю Я and а б в г д е ё ж з и й к л м н о п р с т у ф х ц ч ш щ ъ ы ь э ю я – 33 letters. Chances are if you read Cyrillic at all this is the version you were taught, and it is of course used by roughly twice as many people as the other five versions put together. But of those 33 letters, only 23 – Аа Бб Вв Гг Дд Ее Жж Зз Кк Лл Мм Нн Оо Пп Рр Сс Тт Уу Фф Хх Цц Чч and Шш – are common to all six alphabets; Ии is used by all but Belarusian; Йй Ьь Юю and Яя are used by all four of the more eastern orthographical tradition; Щщ also by Bulgarian and Ukrainian; Ёё Ыы and Ээ only also by Belarusian; and Ъъ is only otherwise found in Bulgarian (but used there for a completely different purpose).

OK, so who can draw me a nice Venn diagram of all this?