|Base item||war hammer|
|Damage vs. small||1d4+1 x2|
|Damage vs. large||1d4 x2|
|Base price||200 zm|
Ogresmasher is an unaligned war hammer that does +1d5 to hit and double damage against ogres. Since it's based on a weak base item, and does its extra damage to a class of monster that's neither particularly common, nor especially dangerous, Ogresmasher is often considered the most worthless artifact weapon. (A regular +0 long sword does more damage to ogres than +0 Ogresmasher, and given its extremely limited use, enchanting it would be foolish.)
In SporkHack, dNetHack, and UnNethack, it sets the wielder's CON to 25 (this effect is also in development version which will become NetHack 3.6.1) and deals an extra +d4 damage to all monsters. It also has a 50% chance of instantly killing ogres. This makes it only very slightly less pointless.
In dNethack, characters who aren't capable of two-weaponing and have no need of the second weapon slot can get increased max HP by keeping Ogresmasher in the off-hand. The 25 CON will grant a 14 CON character around 5/3 as much health, since it applies retroactively to all health gained from levelling up.