GURPS - Russia

From their website:

"GURPS Russia presents the Russian world from its beginnings in the 10th century to its new beginnings in the early 18th. In this book, the GM will find complete details on the history, folklore, and daily life not of the Soviet Union or of the Imperial Age, but of medieval Russia – a culture that seems all but forgotten in the twentieth century, overborne and overshadowed by the U.S.S.R. To most Westerners, the word "Russia" is synonymous with communism, nuclear war, competing space programs, and WWI-level farm equipment serving in the fields of The People.

This book puts characters into the Russia of the Middle Ages, from the 10th century to the 18th. It also opens up the world of Russian folklore and fairytales, where all sorts of interesting – and sometimes frightening – creatures dwell."