Gary Jones

Can add multiple calendar widgets – each of them set to different categories (or All Categories).
The tooltip on the per-day links shows only post titles from that category, and when you click on the calendar link to bring up the day archive of posts, only posts from that category are shown.

Calendar Category

Un-registers the default Calendar widget, and registers a new one which supports showing only those posts in certain (or all) categories.

Sergio

Removes category base from your category permalinks (optional). By default is enabled. 
Removes parents categories from your category permalinks (optional). 
Removes tag base from your tag permalinks (optional).
The three options above are optional and generate their own rewrite rules.
Compatible with WPML Plugin and WordPress Multisite.
Read the <a href="https://wordpress.org/plugins/wp-no-base-permalink/faq/" rel="ugc">FAQ</a> before use.

WP No Base Permalink

It solves the main issue with category permalinks. Simple and effective.

Does the job!

Removes category base or parents categories or tag base from your permalinks. Compatible with WPML Plugin and WordPress Multisite.

Calendar Category vs WP No Base Permalink