Voting With Software... as described in Harrison Owen's OpenSpaceTechnology/UsersGuide.
Software can be downloaded for free from http://www.openspaceworld.org but each meeting/event usage is to be paid for individually, on the honor system, as explained by the software developers at the downloading page.
Direct link to the downloading page: http://www.openspaceworld.org/wiki/wiki/wiki.cgi?MultiVoterSoftware
See also MichaelHerman?'s notes on NonConvergence, variations of which many experienced practitioners find easier, more organic, and more helpful in closing all shapes and sizes of OpenSpaceTechnology meetings and events.