sundiro50: They're actually JellyFish match files. Basically they contain game notation so that you can open and review the game on a software that supports that format. http://www.paulspages.co.uk/bgreplay/
(hide) If you want to play a game with an opponent of a similar level, you can define a required BKR range for a new game invitation. Then nobody with a BKR outside this range will be able to see/accept it. (Katechka) (show all tips)