Steve Grunwell

<a href="https://codex.wordpress.org/Excerpt" rel="nofollow ugc">WordPress post excerpts</a> can be a great way to hand-craft the summary of your content. Unfortunately, writing post excerpts isn’t as nice of an experience as what you find elsewhere in WordPress. Want to include links in your excerpts, or bold some text? Hopefully you know some HTML!
Advanced Post Excerpts is designed to change that, by giving your editors an easy, intuitive interface for writing great post excerpts.
For complete details and/or to contribute to ongoing development, please <a href="https://github.com/stevegrunwell/advanced-post-excerpt" rel="nofollow ugc">visit this project on GitHub</a>.

Advanced Post Excerpt

Replace the default Post Excerpt meta box with a superior editing experience.

Stephanie Leary

Creates widgets that display excerpts from posts or pages in the sidebar. You may use ‘more’ links and/or link the widget title to the post or page. Requires <a href="http://blog.ftwr.co.uk/wordpress/page-excerpt/" rel="nofollow ugc">Page Excerpt</a> or <a href="http://www.laptoptips.ca/projects/wordpress-excerpt-editor/" rel="nofollow ugc">Excerpt Editor</a> for page excerpts. Supports <a href="http://robsnotebook.com/the-excerpt-reloaded/" rel="nofollow ugc">the_excerpt Reloaded</a> and <a href="http://sparepencil.com/code/advanced-excerpt/" rel="nofollow ugc">Advanced Excerpt</a>.
Now on <a href="https://github.com/sillybean/Post-and-Page-Excerpt-Widgets" rel="nofollow ugc">GitHub</a>.

Post and Page Excerpt Widgets

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

Advanced Post Excerpt vs Post and Page Excerpt Widgets