I haven't tested it out personally, but Prefinery might fit the bill: http://www.prefinery.com/ http://www.prefinery.com/ I think their free plan accommodates

I haven't tested it out personally, but Prefinery might fit the bill: http://www.prefinery.com/ http://www.prefinery.com/ I think their free plan accommodates 50 testers. You could also set up a private forum which would allow you to post new versions and allow beta testers to leave and discuss feedback.