This is a simple module provide the way to display the main-menu inside the block, when the user on any page which belong to main-menu. This will list all sub-menu with maximum depth/level.
As per the screen-shot, we have main-menu "test" with the sub-menu "secondary test" and "secondary test !!", when the user on an of this three pages i.e. test, secondary test and secondary test !!, it will build the block content where it display parent menu from menu-menu and all it`s sub-menu(with maximum depth/level). Set title of the block equal to parent menu name from menu-menu. In this example "test" is parent menu so block title is "test" all the child of test menu, i.e. secondary test and secondary test !! are listed in the block.
Link to project at Drupal git.