The User Control Zone has been made as a replacement for the WebPart Zone, which renders all its content in cascaded tables.

On every page layout several DropDown-Lists can be placed to select a User Control. A usercontrol wraps a webpart or another module with dynamic character.

The listed User Controls are the ones you have in the referenced UserTemplates library.

User Controls must be created by a developer with knowledge of accessibility and need to match the criterias of the WCAG10.