Calligra Stage is an easy to use yet still flexible presentation application. You can easily create presentations containing a rich variety of elements, from graphics to text, from charts to images.
Browser requirements: Google Chrome, Mozilla Firefox, Safari. File management (open, save, and edit Calligra files) available via cloud storage services conntected to your rollApp account: Dropbox, Google Drive, Box.
Very slow sometimes and not very user-friendly.