Hi. The Story Map collection is a custom app we created in order to showcase theme-based mini-galleries of stories. You can find the collections we have released so far here. These look like Cascades especially because they have a cover page, but they aren't created using Cascade. We'd like to eventually enable anyone to create a collection but this is just in the R+D phase currently, so the collections we have released are rather like prototypes.
You can make galleries of items in ArcGIS and share them. This can give you a somewhat similar look and feel to what you have posted above. These can also be embedded. It all starts with a group in ArcGIS Online. Groups contain items, like web maps and web apps. You can create groups (requires ArcGIS Online subscription) or work with groups that other people have created, like this one I curate. You can share a group as a link or embed it in a website. You can also create a gallery from a group by sharing it using one of the Gallery apps (requires ArcGIS Online subscription). Click the Share button on a group to try it out.
Rupert
