This interactive real estate investment calculator evaluates property performance by computing monthly cash flow, cash-on-cash ROI, cap rate, and a 10-year projection of equity and cash flow. Users adjust purchase price, financing, income, and expenses in a React form, with D3.js rendering an animated SVG bar chart of the cash flow breakdown and a multi-line projection chart with hover tooltips. The visualizations use d3.scaleBand, d3.scaleLinear, d3.line, and ResizeObserver for responsive sizing.