Multiparts to Single Parts/Single Parts to Multiparts/Polygons to Lines/Lines to Polygons/Extract Nodes
Geometry tools
Multiparts to singleparts:

This function will convert a multipart polygon with the same object ID to multiple singlepart polygons. This will separate all polygons even if non-contiguous. This has the ability to create simple polygons and lines from the multipart polygon.
Singleparts to multipart:

This function will merge multiple singlepart features (lines, polygons, or points) into one multipart feature based on a unique ID field between the multiple singlepart features.
Polygons to Lines:

This function will convert singlepart polygons to singlepart lines and multipart polygons to multiple singlepart lines.
Lines to Polygons:

This function will convert lines to polygons as well as multipart lines to multiple singlepart polygons.
Extract Nodes:

This function will extract nodes from line and polygon layers and output them as points.