Office Mix is a free PowerPoint 2013/ 365 add-in which can help turn your presentations into interactive online lessons.
Mix provides tools to record you giving your presentation, for instance. You can write on slides as though they were a whiteboard, record audio and video, take screenshots or record what's happening on your desktop. It's all available from the new Mix tab on the PowerPoint ribbon.
You can also include custom quizzes, polls, videos and other apps, direct from the Office Apps store.
Once you've finished - or if you're happy with an existing presentation, and don't need to add new content - simply click the Upload button and it'll be hosted for free at the Mix site.
There are three simple "Permission" options. Mixes can be kept private, or made entirely public. Sensibly, the default is "shareable", which means you can pass the link to whoever you like and they'll be able to browse your work online (not yet on Apple or Android tablets, apparently, although that's due very soon).
Some neat analytics then show you which slides were most popular, and where viewers spent most of their time.
Alternatively, Mix can save your presentation as an MP4 video. The interactivity has to go, of course, but at least it'll be viewable everywhere and on any device.