It doesn't fit your criteria of being open-source/free, but I built Bloomberry (bloomberry.com) as an alternative to Wappalyzer for exactly this use case. It analyzes DNS records, subprocessor lists, DNS traffic data to find the real technologies a company uses. So stuff like you mentioned like Snowflake, and even the enterprise LLMs like ChatGPT/Claude.
If you're looking for something truly free/open-source, you probably have to stitch together various sources. You can analyze job postings to see what technologies they mention on job ads (although this can give u some false postives too as companies love to spam long lists of technologies). You could look at what appears when they search for their domain in subdomain tools, which can often give you a clue if they host stuff like CI/CD internally. And just good old-fashioned snooping around the Linkedin profiles of engineers who work there.
