Cost of Capital Calculator
This simple spreadsheet allows you to compute the relevant riskadjusted discount rate of a project or firm.

Cost of equity according to the Capital Asset Pricing Model (CAPM)

Cost of debt using credit spreads

Implied overall cost of capital (unlevered cost of capital)

Weighted Average Cost of Capital (WACC).
See here for a more comprehensive calculator that allows you to estimate the appropriate cost of capital under different financing policies and capital structures.
The modules Risk, Return, and Cost of Capital and Cost of Capital and Valuation cover the theoretical and practical considerations behind the estimation of the cost of capital in detail.