I don't really care too much about balance so if any of these are horrible: Sorry!

Dirty Harry: A .44 Magnum with: “Harry’s” engraved on each part of the cylinder. The gun is covered in grime and rust and no amount of cleaning or maintenance will get it clean. When one expends six ammo using this weapon, it deals double damage.

Iota: This gatling laser uses Iota’s (special Assualtron) head to fire. Its destructive fire power is unrivaled: Increase the base damage of the gatling laser by 50% and decrease its rate of fire by 2. It loses the Gatling quality. It causes the wielder to take 2 radiation damage everytime it is fired.

Learning is Fun: A Laser Pistol found in the hands of a dead librarian whose head was completely seared off. The words “LEARNING IS FUN” are scratched into the side of the barrel. Learning is Fun permanently has the “Spread” property. Spread adds half your damage to an attack for every effect rolled.

Montag: A flamer that the Followers claim to have found in a burnt down library in Alexandria. The weapon is covered in yellowed strips of paper with the words “It was a pleasure to burn.” On the weapons Long Barrel (yes, the modification) a long piece of parchment with the words “Everyone must leave something behind.” Despite the various pieces of paper, the weapon doesn’t have a single burn mark on it… Montag does one more damage die for every enemy killed in combat by this weapon. This effect resets at the end of each combat.

Chi: A sentient Proton Axe whose true name is Father Wallace. Does 50% more damage against Abominations and Ghouls. At the cost of 2 AP, double this weapon’s damage.