Final answer:
A Resource Calendar is key in project management, defining when resources are available for work, as opposed to other tools like Gantt Charts or Critical Path which focus on tasks scheduling and project duration.
Step-by-step explanation:
A Resource Calendar is a scheduling tool that determines the standard working time and nonworking time for the project, resources, and tasks. This tool is essential in project management as it ensures that resources are allocated efficiently and that potential scheduling conflicts are identified and addressed ahead of time. It differs from a Gantt Chart, which visually represents a project schedule and the dependence between tasks, and the Critical Path, which is a sequence of stages determining the minimum time needed to complete a project. A Work Breakdown Structure, on the other hand, is a tool to divide the project into smaller components or tasks.