Broken link building
Broken link building finds dead links on other websites, then suggests your working resource as the replacement, earning a link while fixing the host's problem.
The workflow is straightforward: identify relevant pages (often resource page link building targets) that link out to a URL now returning a 404, confirm you have or can create an equivalent or better resource, then email the site owner pointing out the dead link and offering yours as a fix. You are doing them a favour, which makes the pitch land far better than a cold link request.
It works because the value exchange is real and the resulting links are editorial and topically relevant. Tools that crawl a target site or analyse competitor profiles can surface dead links at scale, and pages that already linked to a now-defunct resource have demonstrated they are willing to link to that topic.
Be realistic about the numbers. Reply rates are modest, many dead links point to content you cannot credibly replace, and the tactic rewards patience and good outreach more than volume. A related angle is link reclamation, where you recover links pointing to your own broken or moved URLs, which a simple redirect 301 can sometimes fix without any outreach at all.