Lets you see a website and its coding from anytime in the past. Great way to see old code, old links and what changes companies have done over time.
Want to see all sites using the same code, or within the same agency, network or other common code strings, then this is what you can use. It searches the source code, not the text of pages.
Back when it was whois.sc it became a legend, I still use this to check domains as gives easy access to find names for sale and can get access to other domains on the servers.
https://whois.domaintools.com/
The best tool when it comes to understanding a websites IP and network. Very simple to use and has the best database for whois look ups.
https://centralops.net/co/DomainDossier.aspx
Want to crawl another site and see all its links, pages and structure. This is the orginal SEO crawler, it does for free what the other tools charge for, plus it has a lot of extras those other tools don't have.
https://home.snafu.de/tilman/xenulink.html