I only know a little bit, here's what I recall. It overstates my involvement because obviously I remember that better than what other people did.
Anyway, there may be some errors here, but it can get the ball rolling.
Erritis was principally Avellone, with help from Gavin.
Tybir was principally Nathan Long, with help from Gavin.
Rhin was principally Rothfuss, with help from Colin(?) or Gavin, can't remember.
Matkina was Colin.
Callistege was Leanne.
Aligern was Colin (I think).
Oom will be Mitsoda, with help from Gavin.
Blue Tidal Mere ("puzzle-breaker"/mind-worms), Indigo (whale), Gold (dying "your grace"), Kholn Village, and Inifere were me.
Red Tidal Mere (Oasis) was Adam. So, I think, was Ossiphagan (the one where you meet Mazzof).
Silver Tidal Mere (Endless Battle with the priest) was Nathan, and so I think was the one where you are going through a dungeon, and the one with the Haref.
The Moon one was Colin.
The Sorrow was Colin, so was the Genocide and Blob of Three.
Inifere was me, so were the Council Clerk, the three philethis, and Loyhan Stolls.
Sn'erf was Gavin.
The RPG Codex one (with incline/decline) was Colin.
Minecraft, Ouya, the nodule in the Bloom, and the crazy colors one were mine. I can't really remember them all that well.
Intro was Colin, so were the characters in the Third Eye.
I did the death slides.
Adam did the ending slides.