Which AWS tool provides visualizations of past AWS spending and projections for future costs?

Cost Explorer is the correct answer because it is specifically designed to visualize and analyze your AWS costs and usage over time. It provides interactive graphs and customizable reports to help you understand past spending patterns and forecast future costs. AWS Cost and Usage Report (CUR) provides comprehensive data sets of your AWS costs and usage, but it's a raw data source, not a visualization tool itself. You'd typically use other tools or services to analyze CUR data. AWS Budgets allows you to set custom budgets and receive alerts when your costs or usage exceed your thresholds, but it doesn't provide the detailed historical visualization and forecasting capabilities of Cost Explorer. Amazon CloudWatch is a monitoring service for AWS resources and applications, not primarily for cost analysis or forecasting.