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.

ircf

This plugin provides the following features :
<ul>
<li>A [fullcalendar] shortcode with custom parameters to be inserted in your pages/posts</li>
<li>An admin page where you can define a custom HEAD and BODY template for the [fullcalendar] shortcode</li>
<li>By default FullCalendar 3.4.0 JS+CSS is loaded locally, your can change the version and/or load from cdnjs by setting the HEAD template (WARNING : Setting the HEAD template will remove the default FullCalendar JS+CSS loading)</li>
<li>A default BODY template to display a Google Calendar (just fill in your API KEY and your Google Calendar ID)</li>
</ul>

FullCalendar

Display and customize one or many Google calendars. A non-official WordPress plugin for the (https://fullcalendar.io/) Open Source project.

Google Calendar Widget vs FullCalendar