Type a whole number and get it written out in English and Russian words, plus its Roman-numeral form (for 1–3999). Handy for cheques, contracts and learning.
Up to the trillions for words; Roman numerals cover 1–3999 by convention.
Yes — it uses the correct gender and plural forms, e.g. одна тысяча, две тысячи, пять тысяч.
Standard Roman numerals have no symbol above M (1000) using subtractive notation, so 3999 (MMMCMXCIX) is the usual maximum.