ChemApp is a programming tool from the area of computational thermochemistry. It is a library consisting of a rich set of subroutines, based on the thermodynamic phase equilibrium calculation module of ChemSage. It permits the calculation of complex, multicomponent, multiphase chemical equilibria and their associated energy balances. ChemApp is available as object code for a wide range of platforms and as a shared library/DLL. ChemApp "light" is the free version of ChemApp, and although it is restricted in two ways compared to the regular version, it gives you almost the same functionality.
Ghemical is a molecular modelling software package with some nice 3D visualization tools. It supports methods based on both molecular mechanics and quantum mechanics (using MOPAC7, and MPQC for QM). The geometry optimization (for MM and QM) and molecular dynamics (for MM) algorithms are included. Ghemical is written in C++, and hopefully offers a good framework for a generic freeware molecular modelling tool.
VMD (Visual Molecular Dynamics) is designed for the visualization and analysis of biological systems such as proteins, nucleic acids, lipid bilayer assemblies, etc. It may be used to view more general molecules, as VMD can read standard Protein Data Bank (PDB) files and display the contained structure. VMD provides a wide variety of methods for rendering and coloring a molecule: simple points and lines, CPK spheres and cylinders, licorice bonds, backbone tubes and ribbons, cartoon drawings, and others. VMD can be used to animate and analyze the trajectory of a molecular dynamics (MD) simulation. In particular, VMD can act as a graphical front end for an external MD program by displaying and animating a molecule undergoing simulation on a remote computer. VMD uses OpenGL and OpenGL Programmable Shading Language for high performance rendering of large structures.
Fityk is nonlinear curve-fitting and data analysis software. It allows data visualization, separation of overlapping peaks, and least squares fitting using standard Levenberg-Marquardt algorithm, a genetic algorithm, or Nelder-Mead simplex method. It knows about many functions (mostly bell-shaped, like Gaussian, Loretzian, Pearson 7, Voigt, Pseudo-Voigt, and Doniach-Sunjic) and user-defined functions can be easily added. It also enables background subtracting, data calibration, and task automation with a simple script language. It is mainly used to analyze powder diffraction patterns, chromatography, photoluminescence, infrared, and Raman spectroscopy, but it can be used to fit analytical functions to any kind of data.