SINDA/FLUINT (Systems Improved Numerical Differencing Analyzer / Fluid Integrator, formerly SINDA '85) is a computer code used to analyze thermal/fluid systems that can be represented in finite difference or lumped parameter form. In addition to conduction and radiation heat transfer, the code is capable of modeling steady or unsteady single- and two-phase flow networks, their associated hardware, and their heat transfer processes. Because it is generalized, versatile, and user-extensible, SINDA/FLUINT is a standard in the aerospace industry for modeling thermal control systems. It is also used in the automotive, commercial aircraft, electronic packaging, petrochemical, and process industries.SINAPS (SINDA Application Programming System) is a complete graphical user interface to SINDA/FLUINT. SINAPS is a schematic-oriented pre- and postprocessor that brings modern visualization methods to a simulation code that lacks geometric constraints. Together, these unique tools are able to accommodate higher-order (perhaps vehicle-level) modeling, indefinite or parametric geometries, and other problems inappropriate for geometry-based CAD (computer-aided design), FEM (finite element method), and CFD (computational fluid dynamics) codes.In this paper, recent improvements to SINDA/FLUINT and SINAPS are described along with developments currently in progress. These improvements include the addition of a multiple-constituent modeling capability to FLUINT, and the gradual merging of SINDA/FLUINT functionality into SINAPS, yielding a completely interactive and graphical environment for the development and fine-tuning of thermal/fluid network models.