The author created a tool called Hacker Trends, which indexes 18 years of Hacker News comments and allows users to see how topics, tools, and people have trended over time. The tool provides a chart showing the frequency of mentions of a particular term, as well as the actual stories and comments behind the trends. The author also created a separate page for 'Who is Hiring?' posts, which shows the distribution of programming languages over time. The tool is built on Upstash Redis Search and allows users to compare terms and see the exact posts and comments from a particular time period.