oEmbed allows you embed a widget from thousands of websites with a single URL. It uses the open oEmbed Standard to access any website that supports it. For example, you can easily embed the following widgets: Twitter posts, YouTube videos, and so much more.
oEmbed is an open standard protocol. When a website support this standard, the oEmbed stack will query an API with your supplied url. If that website supports the standard, they should return HTML embed code. Its pretty cool when a website supports it.
Below are just a handful of examples of things that you can embed with oEmbed. Here is a great list of popular websites that support oEmbed. However, Embedly does support a few embeds for sites that do not support oEmbed natively. I have added support for a few of the most popular of these as well such as Twitter timelines, Google Maps and Instagram posts.
Note: I regret to inform you that Facebook has decided to remove support for the open oEmbed standard for Facebook. There is a new API that requires a complete overhaul. There is no ETA for this at this time.
If some of the embeds are not working in your browser, it could be a content blocker stopping the embeds from being displayed.