Chimera Grid Tools (CGT) is a NASA-developed software package for performing computational fluid dynamics (CFD) analysis utilizing the Chimera-overset-grid method. For modeling flows with viscosity about geometrically complex bodies in relative motion, the Chimera-overset-grid method is among the most computationally cost-effective methods for obtaining accurate aerodynamic results.CGT contains a large collection of tools for generating overset grids, preparing inputs for computer programs that solve equations of flow on the grids, and post-processing of flow-solution data. The tools in CGT include grid editing tools, surface-grid generation tools, volume-grid-generation tools, utility scripts, configuration scripts, and tools for post-processing (including generation of animated images of flows and calculating forces and moments exerted on affected bodies). Tcl is used extensively for configuration and scripted coordination of these tools.One of the tools, denoted OVERGRID, is a Tcl/Tk graphical user interface (GUI) that serves to visualize the grids and flow solutions and provides central access to many other tools. The GUI facilitates the generation of grids for a new flow-field configuration. Tcl scripts that follow the grid generation process can then be constructed to mostly automate grid generation for similar configurations.CGT has spawned a whole ecosystem of commercial support tools, which tend to use Tcl as well, by companies such as Pointwise and Altair.