Google Slides is a simple tool for making slide-show presentations. You can work on the slide show on your own or you can work with a team of other users. You need a Google Drive account to access the software.
Haiku Deck is a simple visual presentation tool and app that enables you to export your presentations to PowerPoint or Keynote. Haiku Deck also contains presentation templates and an image gallery.
Prezi enables users to create and store in the cloud or on a desktop. It is a good tool for short presentations and/or when you want to show visual relationships between concepts. It works best with a good WIFI connection.
Note: you have to purchase a licence if you want your presentations to be private.