Manager is a set of modules focused on "content manager" users, that is, users that maintain the content of a website (adding, editing and deleting nodes, managing comments, etc), but are not site admins (don't have to worry about views, site settings, content types settings, etc). The objective is to let things simple even for users that aren't familiar with Drupal.
The Main Manager modules provides a page (generated with Views Bulk Operations) that allow users to easily perform the most common actions related with their nodes. It's replaces the default "/admin/content/node" page.
Manager's Bar is an admin-bar designed for users that aren't familiar with Drupal. It is like the default "Navigation" menu, when we cut off everything that doesn't matter to this users, and it looks like some known admin-bar-modules, like Admin Menu, but a lot more simple.
Manager's Page improves the "/admin" page providing quick links to add and edit nodes of the most important content types, defined by the administrator.