axenso

You can enable a tooltip that shows info about user/author when you rollover/click on related avatar.
Let’s speak clearly: if you are loooking for a plugin that enables the standard Gravatar hovercards, this is not the plugin right for you. Please look for another one.
When you rollover/click on an avatar (e.g. of a comment author), a tooltip popups and shows:
<ul>
<li>some additional links if the author is a registered user: e.g. to user post archive, to user external website, to user blog (if multisite)</li>
<li>some info from Gravatar if author is registered to that service: e.g. location, “about me” description, websites, other account pages (facebook, twitter….)</li>
</ul>
In plugin settings you can set up the javascript and css main options.
The plugin comes with some filter hooks, so you can customise the tooltip content at all.
The plugin uses <a href="http://craigsworks.com/projects/qtip2/" rel="nofollow ugc">qTip plugin for jQuery</a>.

Avatar Tooltip

To show a tooltip with info (member info and Gravatar profile) when you mouseover/click on an avatar.

Nico Danneberg

Adds explaining tooltips querying their content from a <a href="https://www.mediawiki.org" title="see MediaWiki docs" rel="nofollow ugc">MediaWiki</a> installation, e.g. <a href="https://www.wikipedia.org" title="see the well-known Wikipedia" rel="nofollow ugc">Wikipedia.org</a>. Therefore shortcodes can be used in Posts and Pages to mark keywords and link them to public Wiki pages. The well-known package of <a href="https://calebjacob.github.io/tooltipster/" title="Tooltipster rocks :)" rel="nofollow ugc">Tooltipster</a> is used to create the nice and themable tooltips.
Main features of the current version are:
<ul>
<li>Setup at least one wanted Wiki base and several other options at a backend page</li>
<li>Integrate the Wiki tooltip in Posts and Pages using a handy popup in Gutenberg editor or simple shortcodes</li>
<li>Shortcodes can be created by a <a href="https://codex.wordpress.org/TinyMCE" rel="nofollow ugc">TinyMCE</a> plugin, too</li>
</ul>

WP Wiki Tooltip

Adds explaining tooltips querying their content from a MediaWiki installation, e.g. Wikipedia.org.

Avatar Tooltip vs WP Wiki Tooltip