Poco

This plugin installs a widget for showing a Google Calendar agenda on the sidebar. 
Once installed it adds a sidebar widget called ‘Google Calendar’ that may be dragged into your sidebar. 
Each widget can be configured with a ID of the calendar feed, a title, and the number of agenda items to show.
The calendar feed ID is the ID next to ‘Calendar ID:’ in the Google Calendar settings.
Multiple widgets can be used on the same page and each one can reference a different feed.
See also <a href="http://notions.okuda.ca/wordpress-plugins/google-calendar-widget/" rel="nofollow ugc">http://notions.okuda.ca/wordpress-plugins/google-calendar-widget/</a>

Google Calendar Widget

This plugin installs a sidebar widget that can show the upcoming events from a Google Calendar feed.

topmba

abwebgorohovets

This plugin adds <a href="https://schema.org/Event" rel="nofollow ugc">schema.org’s event markup</a> to All-in-One Event Calendar’s events.
According to <a href="https://developers.google.com/search/docs/guides/intro-structured-data" rel="nofollow ugc">Google</a>, when you provide structured data markup for your online content, you make that content eligible to appear in two categories of Google Search features: 
* Rich results—Structured data for things like recipes, articles, and videos can appear in Rich Cards, as either a single element or a list of items. Other kinds of structured data can enhance the appearance of your site in Search, such as with Breadcrumbs, or a Sitelinks Search Box. 
* Knowledge Graph cards—If you’re the authority for certain content, Google can treat the structured data on your site as factual and import it into the Knowledge Graph, where it can power prominent answers in Search and across Google properties. Knowledge Graph cards appear for authoritative data about organizations, and events. Movie reviews, and movie/music play actions, while based on ranking, can also appear in Knowledge Graph cards once they are reconciled to Knowledge Graph entities.

Ai1ec Rich Snippets

Make your All-in-One Event Calendar events more discoverable in Google (and other) search results by adding rich snippets to them.

Google Calendar Widget vs Ai1ec Rich Snippets