From the website:
Helios offers verifiable online elections.
We believe democracy is important, whether it’s your book club, parent-teacher association, student government, workers’ union, or state. So we’ve made truly verifiable elections as easy as everything else on the Web.
From the FAQ:
What makes Helios different/better than other voting systems?
Helios is truly verifiable. Each voter obtains a smart ballot tracker which can be checked against the Ballot Tracking Center to ensure that the ballot was received and tallied appropriately. What this means is that no one, not even the administrators of the Helios Voting system, can alter your vote.