PlusThat is a free Chrome extension developed by PlusThat that falls under the category of Browsers and the subcategory of Add-ons & Tools. This extension allows users to read and write public comments and private messages on any webpage using a single PlusThat account.

To use PlusThat, simply install the extension and open the Chrome side panel. There are three ways to open the side panel: right-click on any webpage and select the PlusThat context menu entry, click the button to the left of your avatar in the Chrome address bar and choose "PlusThat" from the drop-down list, or use the shortcut Ctrl+Shift+9 (Cmd+Shift+9 for MacOS).

One important aspect to note is the privacy of PlusThat. The extension requires permission to view your browser history, but it only looks at the URLs and titles of the pages you browse. It does not have access to any sensitive data on the page or track your browsing activity. No URL is saved to PlusThat unless you interact with it by adding a comment or participating in a private message thread.

Overall, PlusThat is a useful extension for those who want to engage with web content by leaving comments and having private conversations. Its simple and accessible interface makes it easy to use for anyone using the Chrome browser.