Calico is a tool for performing COCOMO and COSYSMO calibrations.
Based on data describing some of your completed projects, Calico will calculate the optimum estimating equations for your environment.
Calico also lets you modify any of the ~4,000 numbers that define a COCOMO or COSYSMO model -- you can add Cost Drivers, edit the Effort Multipliers, change the equations, change the effort distributions, etc.
Click here to download an Excel spreadsheet that will do simple COCOMO calibrations. It doesn't have the power of Calico, but you can modify it to meet your needs.
Click here for a PowerPoint presentation that introduces COCOMO Calibration.