It is a 3 rank perk tracking your fighting and killing activities. Under the hood it has 6 more perks with each having 7 ranks. They get ranked up while you kill stuff using a certain weapon skill (like small guns, melee weapons, etc). And there is a mastery perk with 3 ranks that get ranked up when you max out two or more weapon skill specific perks. I have added a lot of badass shout outs to give you a feedback when you gained a rank up (because the perks are invisible).
The whole mod does never ever run scripts long in GameMode. Everything is accomplished with callbacks / events only. So the performance impact is as low as possible.
You can download the mod from fallout3.nexusmods.com by search for MME Relentless Warrior Perk.
Have a nice day and enjoy the mod