Based on its naming convention, is a Java Archive (JAR) file typically associated with the Minecraft modding community . Version 1.8.9 is widely considered the "golden era" for Player vs. Player (PvP) gameplay, and clients like "Raven" (specifically Raven B+ or B3) are popular "ghost clients" used to enhance performance and provide discrete gameplay advantages.
Minecraft updated past version 1.8 many years ago, yet 1.8.9 remains incredibly popular. The reason is the . File name- Raven-BS-Client-1.8.9.jar