This document discusses constructive cost model (COCOMO) tools for estimating software project costs. It describes the basic, intermediate, and advanced COCOMO models which estimate effort based on project size, team size, and cost drivers. The limitations of the basic COCOMO model are outlined. COCOMO II is presented as an improved model that can estimate costs for various project types by using scaling factors and effort multipliers across three modules. Examples of COCOMO estimation tools are provided.