One of the 25 tools is Slideshare. With Slideshare, you can upload PowerPoint presentations, tag them and share them with others. You can also synchronize them with an audio file to create a narrated presentation.
Another free tool (not featured in the ’25 tools’) which has similar features is authorSTREAM.
I have tried both and they work great. I had uploaded a PSLE Chinese Oral presentation to authorSTREAM last year and it has an amazing 7000+ hits as of today!
Try using them in teaching! You can also get your pupils to upload their PowerPoint slides and share them with their classmates. Another way is to upload pupils’ slides yourself and embed them in the class blog or equivalent.