Hacker News: Hide Old Comments is a Chrome extension developed by Patrick Walsh. It falls under the category of Browsers and specifically belongs to the Add-ons & Tools subcategory. This extension provides users with the ability to collapse old comments based on their preferences.

With Hacker News: Hide Old Comments, users can automatically collapse comment threads that contain older comments when they revisit an interesting discussion. The extension injects a small form at the top of the discussion thread, allowing users to conveniently bulk-collapse all comment trees that do not have a comment newer than the selected time.

This Chrome extension is free to use and is a handy tool for those who frequently visit Hacker News and want to hide outdated comments to focus on the most recent discussions.