Circular Chess is, as is to be expected, modern chess played on a circular board. There are very few changes to the rules of modern international chess (no castling, no en passent). It was invented in 1983 and has a small following. The game is derived from Byzantine Chess, a medieval Shatranj variant, and both games are included in this .zrf.
 
Unfortunately, the game as implemented is on a very large (600x600) board, so you will need to have your display properties set to at least 1024x768 to play.