Thoses plugins must be copied inside KiCad's python plugins directory (~/.kicad_plugins or /usr/share/kicad/scripting/plugins/ for Linux). Most of them use python plugin (Action plugins) in KiCad. This feature is enabled in daily builds of KiCad. See https://forum.kicad.info/t/howto-register-a-python-plugin-inside-pcbnew-tools-menu/5540

ViaStitching

A pure python via stitching.

After select "Via Stitching" in Tools menu, choose your options in the interface.

Then the result should be:

CircularZone

A pure python script to create circular zone.

Select a component. This composent will be used as center of the circular zone. If no component is selected, the origin (0,0) will be used as center.

After select "Create a circular zone" in the Tools menu, choose the radius and the type of zone (normal or keep out).

A circular zone will be created. Select it to change properties:

Refill the area (B hotkey) then the circular zone is ready.