A weaponized chain-saw like weapon that was used by the military before the war, most likely in hand to hand combat or as a utility, like a multitool.
The ripper is a chain-blade type weapon that has very high DPS. Unlike its implementation in previous Fallout games, it can execute a powerful slashing attack on command outside of V.A.T.S. thanks to the addition of a separate melee power attack button. It is affected by the same perks as all melee weapons.
A ripper normally inflicts 5 hits per attack in V.A.T.S., making a wounding variant one of the most powerful weapons in the game, but when executing a V.A.T.S. critical attack, it seems to only do 1 hit; this may be a bug. [Source: wikia]
You can download this papercraft template here: Fallout 4 - Ripper Papercraft Free Template Download [Box] [Gavitex] [Ver.2]