I included Fliptrack in my post on The Best Ways To Create Online Slideshows. They’ve just changed their name to Moblyng, appear to have kept all their attractive features, and have made it even more accessible to English Language Learners (and others).
It seems even easier to make a slideshow and it continues to allow you to invite others to collaborate on your creation. Plus, and this is the best addition, you don’t have to register on the site to create slideshows anymore.
The only negative with that last change is that, if students are using a public or school computer, they need to click “Clear Your Personal Info” so that others don’t have access to it. The other alternative is to register with the site, which is easy to do.