Instead of dropping your inventory on death, a grave will be dug in which lies a buried chest with your inventory and experience. The grave will be inscribed with your name and time of death. This helps to keep your things from getting lost or despawning.
All modpack authors are free to use this mod as long as they link the modpack in a comment or PM.
Kudos to DerBaM for creating the original mod: http://www.minecraftforum.net/topic/818831-/#BaMsGrave