keith_wp

After getting annoyed that the default 2017 theme was showing the full post content on every index page, I extended <a href="https://wordpress.stackexchange.com/a/77947/25187" rel="nofollow ugc">this support answer</a> into this plugin that can filter calls to “the_content” and return the post excerpt instead.

Always Show Excerpts

On selected types of indexes, choose to always show the excerpts for a post instead of the full post content.

maztch

Creates widgets that display content excerpts or excerpts from posts or pages in the sidebar. 
You may use ‘more’ links, show featured image, set excerpt length of the post or page.
This also adds an excerpt field to your pages like posts have.
You can show content excerpt, the excerpt or both.
Option to highlight the output added.
<h3>MZ Post and Page Excerpts Widgets Features</h3>
<ul>
<li>Shows posts excerpts.</li>
<li>Shows pages excerpts.</li>
<li>Shows posts content excerpts.</li>
<li>Shows pages content excerpts.</li>
<li>The excerpts length can be customized.</li>
<li>The featured image can be displayed.</li>
<li>Read more text can be customized.</li>
<li>Add page excerpt like posts have.</li>
</ul>

MZ Post and Page Excerpts Widgets

Creates widgets that display excerpts from posts or pages in the sidebar.

Always Show Excerpts vs MZ Post and Page Excerpts Widgets