I'm a bit late on the reply, but indeed, I forgot Ability Checks when I wrote my post. The 3 main "success/fail" roll types in 5E are Attack Roll, Saving Throw and Ability Check. Skills Checks are just a particular kind of Ability Checks for which a skill can be learned and proficiency bonus can be applied.
Also, to add to Niara's list, aside Initiative rolls, Shove/Grappling contests and Perception checks, there's also getting out of Entangle/Ensare-type vines which would require a Strength Check. Still not a massive list, and Hex doesn't shine for its curse half, but rather its damage-dealing half.
