Bratka
Russian slang term used in the same way is "bro" is used by English-speakers. Could be a literal brother but more often refers to a friend. This phrase is also used by Lithuanians and Polish sometimes (usually just youth though).
Person 1- Ey, bratka, whats going on?
Person 2- Na, nothing, bratka. You?
Person 2- Na, nothing, bratka. You?