Kaz Kadalashvili

The WordPress Category Archive Widget Plugin displays a monthly or yearly archive of posts for one specific category. It is very similar to the WordPress Archive except that it just displays one specific category’s posts, not all categories. It can be configured to either show a listing or a dropdown by month or year with or without post counts.

Category Archive Widget

Super Plugin

The Category Archive widget displays a monthly or yearly archive of posts for one specific category.

Michael Adams (mdawaffe)

Just One Category will cause WordPress to display on a category archive page 
only those posts which are direct members of that category, i.e. this plugin 
will exclude from that category page all posts which belong to any of that 
category’s subcategories but do not belong to the category itself.

Just One Category

On a category's archive page, displays only the posts directly in that category, not in any sub-categories.

Category Archive Widget vs Just One Category