The Glaive beam is one of the strongest weapons in FTL, requiring four power. It does 3 damage per room and can cover up to 18 tiles diagonally, the equivelent of 80 pixels. It can instantly take out certant ships. It costs 95 .
This weapon is the easiest way to earn the They Never Saw It Comming achievement.
It is called BEAM_3 in the game files.