Attunements
Attunement Binding
Attunements are sources of power, generated by some unifying ideology. Power concentrates differently in different cases; some Attunements boast hundreds or thousands of members working towards similar goals in very different ways. Some are small bands with a very narrow, local focus. Most lie somewhere in between. Scholars have been trying for centuries to find the underlying law of reality that determines which factors develop into Attunements and which will not. Not one has come close. Every Attunement is easy to explain after its birth. No one has succeeded in predicting new formations with any accuracy.
New Attunement formation is thought to be comparatively rare. Many 'new' Attunements are actually re-formations of philosophies long thought deceased, or variants of other philosophies that forked far enough away to develop their own bonds. That said, surveillance across the planes is not all that scholars could wish, and Attunements could easily be born, serve out their functions, and disband before Nexus scholars even hear rumors of them.
Attunement Powers
Powers are what distinguish an Attunement from a club or a gang. Which powers grow where is a mystery; some Attunement sets manifest exactly what you'd expect, some are so far off the stated goals that onlookers suspect a hidden agenda. Progression, mercifully, is well-studied and linear. Power grows as a function of dedication to the philosophy; adventurers refer to this measurement as "Favor", even where that term is imprecise. It arose from some of the more public and prominent Attunements where it fit perfectly; adventurers being what they are, then lumped every other measure into that box and called it a solved problem.