A quick overview
HyperBlocks is a WYSIWYG editor for sidebar content on Reddit. Its main aim is to allow moderators to easily organise the contents of sidebars in their subreddits in a neat and well-structured way without any prior knowledge of CSS or Markdown syntax. You find a video of HyperBlocks editor in action at the bottom of this page.
You can find the live demo of the editor here. The source code is available on HyperBlocks' GitHub page. To see some discussions related to the editor you might wanna check out this Reddit thread and /r/HyperBlocks.