Create a hanoi tower game.

You'll need a script to keep track of which Rings are on which poles:

 public class RingPositions : MonoBehaviour
 {
     public static List<Ring>[] poles = new List<Ring>[3] { new List<Ring>(), new List<Ring>(), new List<Ring>() };
 }

And a script attached to each ring. Something like this:

 public class Ring : MonoBehaviour
 {
     public int size = 0; // The size of the ring. Larger value = bigger ring
     public int poleNumber = 1; // The pole number this ring is on. Either 1, 2 or 3
 
     bool isBeingDragged = false;
 
     void Start ()
     {
         RingPositions.poles[poleNumber].Add(this as Ring);
     }
 
     void OnMouseDown ()
     {
         // Find the minimum ring size on this pole
         int minSize = 99999;
         foreach (Ring r in RingPositions.poles[poleNumber])
         {
             if (r.size < minSize)
             {
                 minSize = r.size;
             }
         }
 
         // Can only move the ring if it is the minimum size ring on the pole
         if (size == minSize)
         {
             isBeingDragged = true;
         }
     }
 
     void OnMouseDrag ()
     {
         if (isBeingDragged)
         {
             // Update position of this object to follow the mouse
         }
     }
 
     void OnMouseUp ()
     {
         // Find the position of the nearest pole
         int nearestPoleNumber = ..... ; // Either 1, 2 or 3
 
         // Make sure we have dragged it to different pole
         if (poleNumber != nearestPoleNumber)
         {
             // Find the smallest ring on the new pole
             int minSize = 99999;
             foreach (Ring r in RingPositions.poles[nearestPoleNumber])
             {
                 if (r.size < minSize)
                 {
                     minSize = r.size;
                 }
             }
 
             // This ring must be smaller if we can put it on this pole
             if (size < minSize)
             {
                 RingPositions.poles[poleNumber].Remove(this as Ring);
                 RingPositions.poles[nearestPoleNumber].Add(this as Ring);
                 // Change the position to the new pole
             } else
             {
                 // Change position back to the pole it was on
             }
         } else
         {
             // Change position back to the pole it was on
         }
         isBeingDragged = false;
     }
 }

This keeps track of the size of each ring and doesn't allow for placing large rings onto smaller ones. You'll have to fill in the gaps, updating the rings positions when being dragged or moved to the new ring or being moved back to the old ring.
You also need a way of finding which pole is nearest when you drop the ring. I suggest using a gameObject for each pole and Vector3.Distance to find the nearest.

A Unity version of this game can be found at:

https://juanborgesv.itch.io/tower-of-hanoi

Source code is also available at https://github.com/juanborgesv/TowerOfHanoi