To highlight the main differences between both packages:
ESPResSo:
* Lead development at the Institute for Computational Physics in Stuttgart, Germany
* Unique features:
* Various methods for electrostatics and magnetic interactions
* Coupling of the particles to mesoscopic fluid methods to incorporate hydrodynamic interactions
* Particles can form flexible or rigid agglomerates
ESPResSo++:
* Lead development at the Max-Planck-Institute for Polymer Research in Mainz, Germany
* As for the unique features of ESPResSo++, maybe Torsten is the better person to reply
Olaf