Warmonger

 is a perk added to Fallout 3 with the Broken Steel DLC.

With this perk, all custom weapon types become available to you without the schematics. Taking this perk immediately gives you the level 3 schematics for all weapon types you did not already have. This perk can either be extremely useful or a complete waste: it is useful, for example, if you have missed your chance to get some of schematics (Herbert Dashwood killed, Doc Hoff killed, etc) and can also save you the 30 Nuka Cola Quantums required for Sierra Petrovita's schematic. But, since the full benefit of this perk can be acquired simply through exploration and trade (especially by the time you get to the required level), it's merely a convenience unless you want to create a truly absurd stockpile of Nuka Grenades.