By Fire and Sword is the free version of a commercially published set of rules for the wars of Polish Lithuanian Commonwealth against Turkey, Muscovy, Sweden, the Crimean Khanate and the Cossacks.
I fell in love with the period some years ago when I read a trilogy of books — With Fire and Sword, The Deluge and Fire In The Steppe — that was set in the period. The Polish author, Henryk Sienkiewicz, won the Nobel Prize for literature.