Java simulation of the Kilobot system by Rubenstein et al. in "Programmable Self-Assembly in a Thousand-Robot Swarm"
http://www.sciencemag.org/content/345/6198/795.full.pdf?keytype=ref&siteid=sci&ijkey=6HDqxr.PcBD7o
http://www.sciencemag.org/content/suppl/2014/08/13/345.6198.795.DC1/Rubenstein.SM.pdf
Graphical interface made with Netbeans.