This module is no longer maintained. Similar functionality is available in modern versions of foundry by the combination of the Drag Ruler and Routinglib modules.
This module adds a new ruler option in the tokens tab. While it is active, a ruler will be drawn from your selected character to the location under the mouse, automatically routing around walls, to make navigating twisty corridors easier for players.
Copy https://raw.githubusercontent.com/mothringer/foundry-vtt-pathfinding-ruler/main/module.json into the module installer manifest field.