HFSM2 is a feature-rich header-only hierarchical FSM framework written in C++ using template meta-programming, distributed under permissive MIT license.
Originally conceived as a traditional hierarchical state machine framework, over the years it evolved into a powerful decision making system, incorporating a variety of features usually found in dedicated AI formalisms.
HFSM2 is an evolution of HFSM, and being actively developed with the new features to empower the developers in embedded, robotics, game development, and other high-performance domains.
doc.hfsm.dev is the new home for HFSM2.
Older GitHub Project Wiki might have more information on a particular topic.