  Based on a recently introduced analytical strategy [Hollingshead et al., J.
Chem. Phys. 139, 161102 (2013)], we present a web applet that can quickly and
semi-quantitatively estimate the equilibrium radial distribution function and
related thermodynamic properties of a fluid from knowledge of its pair
interaction. We present a detailed description of the applet's features and
intended workflow, followed by a description of how the applet can be used to
illustrate two (of many possible) concepts of interest for introductory
statistical mechanics courses: the transition from ideal gas-like behavior to
correlated-liquid behavior with increasing density and the tradeoff between
dominant length scales with changing temperature in a system with ramp-shaped
repulsions. The latter type of interaction qualitatively captures distinctive
thermodynamic properties of liquid water because its energetic bias toward
locally open structures mimics that of water's hydrogen-bond network.
