Precision. Panels Everywhere. Panels Everywhere is an advanced method to completely do away with Drupal's restrictive blocks system and instead use the much more freeing Panels Layout system to control how your pages look.
Panels Everywhere modifies the page as it is being rendered to 'wrap' the content in a display and can even take over your page theme to do away with the need for a page.tpl.php. Doing this requires that you set up a few things properly, because Drupal is not really designed for this kind of behavior. Chaos tool suite. This suite is primarily a set of APIs and tools to improve the developer experience.
It also contains a module called the Page Manager whose job is to manage pages. In particular it manages panel pages, but as it grows it will be able to manage far more than just Panels. For the moment, it includes the following tools: Panels. An Overview of Panels The Panels module allows a site administrator to create customized layouts for multiple uses.
At its core it is a drag and drop content manager that lets you visually design a layout and place content within that layout. Integration with other systems allows you to create nodes that use this, landing pages that use this, and even override system pages such as taxonomy and the node page so that you can customize the layout of your site with very fine grained permissions. Integration with CTools module.