Before The Taken King, the following factions allowed you to gain reputation to purchase new weapons and equipment:
Vanguard, Crucible, Dead Orbit, Future War Cult, New Monarchy, Crota's Bane, Queen's Wrath, House of Judgement, and Iron Banner
After The Taken King was released, the lonesome vendor that nobody ever visits, the Gunsmith, now has reputation. However he does not possess any items that are purchasable through increasing your rank.
Does anybody know what the reputation for the Gunsmith will be used for?
My only speculation is that it would be similar to the Cryptarch where you obtain additional items for each rank after rank 3.
Best Answer
The gunsmith has his only weekly event called Armsday which allows players to order from a selection of 6 legendary weapons of random type and manufacturer. The ordered weapon is delivered to you via the Gunsmith the following Wednesday (Armsday), the weapons perks are randomized and are not the same for every player. At this time his weekly field-test weapons and weapons available for ordering will also change.
Players can start ordering weapons when their reputation with the Gunsmith is at least rank 1. You can place 1 order at rank 1 with the gunsmith and as you raise your rank you are able to place additional orders per week.
He also gives quests at ranks 2 and 3 that gives class-specific rewards. Rank 2 rewards a legendary special weapon, and rank 3 rewards an exotic primary.