A similar website that is specific for History and Global Studies is Power Point Palooza.
All these sites can be very useful when you have not got enough time to build your own slideshow orto look through for ideas for creating your own slideshows.
For History teachers, Tom Richey has wonderful PowerPoint presentations and hundreds of useful videos in his youtube channel.
If you need a tool to assess students' Powerpoint presentations, I would like to share this one with you.
If you are interested in a rubric to assess students' oral presentations following a different format from ppt, this one can help you.