Tim Plunkett recently created a new project for Drupal 8 - Page Manager, which looks set to be the replacement for what was the Page Manager module in CTools from D7.

From the project page:

It supports the creation of new pages, and allows placing blocks within that page.
Like Drupal 7's Page Manager, it provides a concept of "page variants", each with their own selection conditions.
Additionally, it can be used to take over an existing page, like overriding /node/% to change what is displayed when viewing a node. It utilizes the core Conditions, Context, and Blocks APIs to accomplish this.

I'll be keeping a close eye on this project, especially with regards to responsive design in the eventual Drupal 8 Panels module that, at least at this stage I assume, will provide the actual layouts for Page Manager pages.

I'm pretty excited about this project and encourage anyone interested in D8 Panels and Page Manager to jump onboard and lend a helping hand.