Sparanoid

Adds readability.com widget on your site. A must-have plugin if you’re a Readability publisher. This plugin also works fine with multisite enabled WordPress (aka. WordPress Mu).
More information please visit my <a href="http://sparanoid.com/work/readability/" rel="nofollow ugc">site</a>.

Readability Buttons (readability.com)

Adds readability.com widget on your site.

Dana Ross

Read Later Buttons provides a widget and a shortcode for displaying “read later” buttons for the popular apps Instapaper, Pocket, and Readability. It can also display a <a href="https://wordpress.org/extend/plugins/send-to-kindle/" rel="ugc">Send to Kindle</a> button if that plugin is installed, letting your users send your content to their e-reader to enoy when they have the time.
This plugin is designed to function well and look good without much fuss, but it also provides a shortcode and filters so you can control how the buttons look & work.
Shortcode
Use the <code>[read_later_buttons]</code> shortcode to render buttons for every one of the supported services. You can also include the names of one or more services (i.e. <code>[read_later_buttons instapaper pocket]</code>) to just get those buttons. Valid service names are <code>kindle</code>, <code>instapaper</code>, <code>pocket</code>, and <code>readlater</code>.
The shortcode can also display an estimated reading time if you include the “time” parameter (<code>[read_later_buttons time]</code>). The reading time can be combined with service names (<code>[read_later_buttons time instapaper]</code>) and the time will render above the buttons. When including the time estimate, the plugin won’t display all the buttons by default. You need to include the “all” parameter (i.e. <code>[read_later_buttons time all]</code>) in that case. Also, the shortcode has to be used inside “the loop” in order to calculate a time — in other words in a page, post, or the appropriate parts of your theme template.
Filters
<ol>
<li>read_later_buttons_do_css: return false to prevent loading the default CSS (doesn’t affect the Kindle plugin)</li>
<li>read_later_buttons_instapaper: alter the HTML generated for the Instapaper button</li>
<li>read_later_buttons_pocket: alter the HTML generated for the Pocket button</li>
<li>read_later_buttons_readability: alter the HTML generated for the Readability button</li>
<li>read_later_buttons_reading_time: alter the HTML generated for the reading time estimate</li>
<li>read_later_buttons_link: alter or replace the link passed to the read later services (doesn’t affect the Kindle plugin)</li>
</ol>

Read Later Buttons

Adds "read later" buttons to a site. Can send content to Kindle (additional plugin required), Instapaper, Pocket, and Readability.

Readability Buttons (readability.com) vs Read Later Buttons