Here is somewhere between a unique mechanic and feature of spells, tell me if it's what your interested in. The idea is that these spells can carry on when after concentration is dropped. I like the idea of Druids harnessing the forces of nature, but one slip up means that the spell is out of control.
Conjure Tornado (3rd)
Druid
Casting time: 1 Action
Range: 50 Feet
Target: 5 Foot Radius, 50 ft high cylinder centered on a point in range
Duration: 1 Minute, Concentration*
Component: V,S
A pillar of swirling wind appears centered on the point that you choose. Each creature in the tornado's space must make a Strength saving throw. On a failure, a target takes 2d8 bludgeoning damage and is flung up 20 feet away from the elemental in a random direction and knocked prone. If a thrown target strikes an object, such as a wall or pillar, the target takes 1d6 bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a Dexterity saving throw or take the same damage and be knocked prone. If the saving throw is successful, the target takes half the bludgeoning damage and isn't flung away or knocked prone.
On each of your turns after you cast this spell, you may, as an action, move the tornado up to 50 feet to a new point within the spell’s range. The tornado must not double back on itself in a turn. Creatures that the tornado moves through must make saves, and suffer the spell’s effects as normal.
You may spend a bonus action to dispel the spell while you are still concentrating on it. If you lose concentration on this spell during this duration for any reason (fail a save, cast a new concentration spell, choose to stop concentrating) the tornado rages on. When that happens, the tornado joins initiative right after the caster's turn. The tornado moves 50 feet along the ground in a random direction, or direction of the DM's digression, on its turn.