It is often associated with custom modifications (mods), replays, or "champion" builds for strategy games (like Age of Empires or League of Legends ).

A free, open-source alternative that handles almost any compressed format.

Ensure it is actually a .rar and not a double-extension file (like AgrChamp.rar.exe ), which is a classic trick to get users to run malicious code. How to Open It Safely