galaxiusmons

This allows you to quickly create a unique sidebar for any post, page, category page or for all posts belonging to a category. You simply enter a name for the sidebar when you create or edit a post, page or category. Browse to Appearance -> Widgets, find your new sidebar and add some widgets to it.

Galaxius Custom Sidebars

Allows quick creation of unique sidebars for posts, pages and categories.

Trevor Anderson

Split sidebars and widget areas into responsive columns.
Two simple widgets are provided, “Layout: New Column” and “Layout: New Column on New Row”.
Simply place these in your widget area where you’d like to create a new column (split) or new row of columns.
Gutter size and responsive collapse options are available in the Customizer -> Widget Columns panel.

Tuxedo Responsive Widget Columns

Just tested this plugin, and it works exactly as I hoped for. I can now have complex layouts in any widget areas. 
Of course it's best used for horizontal widget areas like footers, etc...



Works perfectly!

Split sidebars and widget areas into responsive columns.

Galaxius Custom Sidebars vs Tuxedo Responsive Widget Columns