aiKit.bt — a small behaviour tree for NPC brains. local BT = require("aiKit.bt") local root = BT.selector("root", { BT.sequence("flee", { BT.condition("hurt", function(ctx) return ctx.health < 0.3 end), BT.action("run away", function(ctx, dt) ... return "running" end), }), BT.action("idle", function(ctx, dt) return "success" end), }) BT.define("myBrain", root) -- name it so a preset's `brain` can use it local tree = BT.new(root) tree:tick(ctx, dt) -- "success", "failure" or "running" print(tree.active) -- the leaf that ran last ("run away") Nodes are plain tables shared by every brain that uses them; what a node remembers between ticks (which child is running, a cooldown) lives on the tree instance, so one definition serves any number of characters. Composites: sequence (all must succeed, in order), selector (first that does not fail), parallel (all children each tick; succeeds when `need` succeed). sequence and selector resume a running child next tick (memory = true) or re-check from the first child every tick (memory = false, the default, so a higher-priority branch can take over at once). Decorators: invert, succeed (always success), cooldown (seconds), timeout (seconds), repeatUntilFail. Leaves: condition (boolean), action (status), wait (seconds).