The ARPS Syndicate Subdomain Center has developed a research project that combines various tools, including Apache’s Nutch, Calidog’s Certstream, OpenAI’s Embedding Models, and some of their own proprietary tools, to uncover an extensive number of subdomains. In order to prevent misuse, they have implemented a limit of three requests per minute. They also acknowledge that there may be occasional periods of downtime and delays due to the overwhelming demand from users and the less than ideal server capacity, humorously likening their servers to a potato-powered hamster.
https://www.subdomain.center/