Graft allows people to distribute their homebrew FoundryVTT content without redistributing the source material it is based on.
For example, suppose I'm writing an adventure that features a custom NPC based on the Monster Manual Bandit Captain creature. I want to beef her up a bit, though, so I set her HP to 105 (instead of 65) and give her the name "The Enforcer". I can share this actor as the following graft:
{
"id": "customEnforcer01",
"type": "Actor",
"pack": "my-actors",
"source": "Compendium.dnd-monster-manual.actors.Actor.mmBanditCaptain0",
"patch": {
"name": "The Enforcer",
"system": { "attributes": { "hp": { "value": 105 } } }
}
}
Importantly, the graft above does not contain any proprietary data that we do not have permission to redistribute (e.g., Monster Manual art, descriptions, etc.). When a user imports this graft on their own server, it clones the Monster Manual Bandit Captain creature (assuming they have the module installed and enabled) and then applies the specified patch to recreate the desired NPC.