we have been building DNSArchive (a DNS repository) and recently launched the web metadata search.

It allows you to look for specific patterns on headers, links and other hard to search parts of sites.

For example, you can search for all sites using PHP/5.2:

https://dnsarchive.net/web-search?q=PHP/5.2

Or WordPress 5.2:

https://dnsarchive.net/web-search?q=%22Wordpress%205.2%22

And things like that. Feedback welcome!