Hollow Hold aka Banana - basic but effective. If your whole body shakes while you hold the position, you're doing it right! Do your best to pin your lower back flush against the ground.
Floor Seated Bottom Up Kettlebell Press - bottom up kettlebells are a great way to increase the challenge of movement without adding load. This is good for swimmers out there with injured/tender shoulders.
Core involved in a wicked shoulder bolstering move!
Palms Up Banded Pull Aparts - warm-up or good for general healthy shoulder movement!
Scapular Pull-Ups - slow and gentle movement through the shoulder girdle. Great for warm-ups and/or general stability
Supine Single Arm KB Shoulder Rotations - activation, pre-hab, rehab and general shoulder bolstering! Slow and controlled.
Strict Toes to Bar - Obviously good for "core", but another sneaky one for working on grip strength! Modify with hanging knee raises, or make harder with a DB between the feet!