RHEO or Reproducing Hydrodynamics and Elastic Objects is a package to model multiphase fluid systems. The authors include Joel Clemmer (Sandia), Thomas O'Connor (Carnegie Mellon), and Eric Palermo (Carnegie Mellon). Bond style rheo/shell, compute style rheo/property/atom, and fix style rheo/temperature all depend on the BPM package. This package requires the GNU scientific library (GSL). We recommend version 2.7 or later. To build this package, one must first separately install GSL in a location that can be found by your environment.