I wrote an HTN planner in C# based around the builder pattern. Maybe someone can find it useful. I'll continue to expand on this and eventually build visual tools, but for now its code-only. https://github.com/ptrefall/fluid-hierarchical-task-network It's the same technique of AI used in Horizon Zero Dawn, Killzone 2/3, Transformers: Fall of Cybertron, and others. It is very expressive in terms of how you can design your decision making, you can apply future prediction and thus plan into the future, while it remains predictable in terms of which decision branches are prioritized, similar to behavior trees. Its also very performant, supports partial planning, allowing you to pause a plan and continue where you left off after the partial plan is completed.