Subfinder
subfinder is a subdomain discovery tool that returns valid subdomains for websites, using passive online sources. It has a simple, modular architecture and is optimized for speed. subfinder is built for doing one thing only - passive subdomain enumeration, and it does that very well.
This tool can scrape subdomains from open sources like DNSdumpster.
Installation
Repo: https://github.com/projectdiscovery/subfinder