I felt especially inspired recently and made the Manyfold Summoner
, a D&D 3.5 PrC (that could probably easily be ported to Pathfinder) that focuses on summoning. To my knowledge, no 3.x PrC that (almost) fully advanced casting focused entirely on summoning. The summon boosts were just part of a package that sometimes involved calling creatures (Malconvoker, Thaumaturgist) or doing casting stuff in general (Master Specialist, Paragnostic Apostle).
The overall goals of this PrC were thus:
-Improve summoning and summonlings without making them too strong.
-Combine and refine the official summoning abilities from 3.5.
-Add enough original content to make it worthwhile.
-Stick to theme.
I acknowledge this PrC may seem or be strong. However, it does what it does well, or at least it should. Is it better than Planar Shepherd, Incantatrix, or/and Dweomerkeeper? Almost certainly not, but such isn't the point. Is it better than the other PrCs that are at least somewhat summoning-related? Quite likely, and that's intentional, due at least in part to a general lack of purely summoning-focused PrCs.
Thankee for your consideration!