ProAct is our planner for direct end-user use in project management and contingency planning. We're building it after extensive experience with SIPE-2 (Wilkins, 1989) and discussions with Austin Tate and Brian Drabble. We rely on untrained end users to create the plan knowledge. Due to the nature of their planning needs, we've made several significant changes to the functionality and representation over other classical planners. These changes have rewarded us with additional benefits. Among the benefits is the advantage of using a fully object-oriented representation. We no longer use an action-net but instead use what we call "object histories" to represent the modifications to objects over the plan. Experiments and formal analyses show that object histories almost always outperform action nets for question-answering (or Modal Truth Criterion (MTC)) and detection of precondition clobberers.