APE is a domain-independent reactive planning system used to build dialogue systems. Turns in the dialogue may include graphical actions as well as typed text. While APE runs fast and is easy to use, it is more powerful than many other dialogue managers because it can handle multi-turn plans, update plans during execution, and generate nested discourse constructs. Although APE is intended for creating dialogues containing hierarchical, multi-turn plans, it can be used to implement any dialogue system. In this paper we describe the motivation for the APE system, its internals and its uses. We illustrate the use of APE with CAPE, an APE-based system that tutors medical students on blood pressure regulation.