I remember there use to be a mod around that allowed you if you got your disposition high enough with anyone. You could have them become your companion and customize their inventory and such to your liking. Such as add weapons or change their clothes. Anyone know the name of this mod? Or know of a mod like this?

Here are some mods that do stuff like this:

Dracandros' Voice by Dracandros
Give Your Orders by TheLys
NPC Commands by Horny Buddha
NPC Functionality by Casey Tucker

Edit: also: Open Inventories by Yacoby

At a more basic level there is " Follow Me " by Shade the Bandit . This is literally only a mod that gets NPC's to follow you and act on basic commands if they like you enough . No sharing of inventory . Also
there is Cutthroat Mods Partners . These are more companion oriented and depend on if there is alignment compatibility between NPC and player .( Yes , they built the old D & D war horse alignment into the game ! )