Diebold, Microsoft and so on want you to use their software and voting machines. The problem is, the value of all intellectual property is dependant on the integrity of the electoral process, and that integrity must be accountable to the general public. That means said software must be visible to the public. Open source. My own election software doesn't even have "sourcecode", it's a fairly human-readable unix shell script.
You can't make billion$ selling voting machines. You can make billion$ selling votes. I'd be happy to make a nice living selling scripting consulting, which is all an election system needs. It doesn't need software at all, but if it's true public freeware you might as well have instant tallies.
Google Hohensee validvote