PC acquaintances

I once read a Reddit post or saw a video where a system of relationship was explained. I am trying to find it again.

Basically, if I remember correctly, every PC would create 3 NPC with whom they have relationships with ( parent, master, rival etc) then they would choose NPC created by other players and decide what was their relationship with them. So you find out during the campaign that the Barbarian brother owes the rogue some money or stuff like that...

Anyone knows what I am talking about?