Wikipedia
DistrictBuilder
DistrictBuilder is an open source computer software developed by Public Mapping Project and engineered by Azavea, a geospatial analysis company, for drawing maps of electoral districts. Using the software, people can create and edit district plans, display demographics and election data, and show additional reference map layers.
In 2010 and 2011, the software was used by a number of citizen groups to present redistricting proposals in some US states. In addition, the software was also used in redistricting competitions organized by Michael McDonald in 6 US states.