Quick Snap - allows you to transform an island or geometry elements by Vertex, Edge Center and Face Center. There are two methods of calling the operator via the keys:

• V - quick start, the nearest transformation element is selected immediately
• Alt+V - here you can safely select the necessary element and change the modes to Island or Element mode

Stack - overlap islands with similar geometry

Weld - [W] connects selected vertices by common vertexes, if there is nothing to connect, it works as Stitch 

• Alt+Weld Button - connect by distance