From the about page:
OpaVote was created in 2011 to provide an affordable and professional quality online voting platform for ranked-choice voting. Although OpaVote supports traditional check-the-box voting as well, it is hoped that organizations will choose to use ranked-choice voting once they understand the benefits and how easy it is to implement in their own elections.
OpaVote uses OpenSTV to count the ranked-choice votes. OpenSTV was created in 2003 and is now the most used and most reliable software for counted ranked-choice votes. Through OpenSTV, OpaVote supports commonly used vote counting methods such as instant runoff voting, Condorcet voting, ERS97 STV, and Scottisch STV.
OpaVote is designed for scalability and reliability. OpaVote uses Google App Engine and Amazon’s Simple Email Service to help ensure that OpaVote can handle web traffic from a large number of voters and to help ensure that emails get delivered to voters. OpaVote supports elections with up to one million voters.
More information, incl. pricing info, is available in the FAQ.
OpaVote is based out of Somerville, Massachusetts.