They are using a beta addon for Connections which I offer, on request, to those who purchased the Pro Pack. They are also using the Slim Plus template which comes as part of the Pro Pack.
I freely give it as a free addon in the bundled price. The reason it is not officially part of the bundle is because I still consider it a beta product. With the release of WP5, my goal for this year is to build it as a block which can be used and configured in the new editor.
You can see it in action on this third part site:
I consider this beta software, though safe to run on live sites. It can be difficult to configure due to the complicate shortcode structure to configure the multiple category setup. If you are familiar with shortcodes it should not be too difficult. They styling is as is, though I can give you CSS to apply you own color (instead of blue).
Hope this helps!