A year ago I started scraping job posts all over the internet. Now I have a database with 600k+ jobs from tens of thousands of companies.
I've extracted which technologies they're using, based on those job posts. This lets one know things that other sites like BuiltWith can't, because they only analyze the frontend of websites.
It can be useful, for example, to know what companies use technologies that your SaaS integrates to, and then to reach out to those companies.
This is still in a closed beta but I reached out to some companies already and got my first customers. If it sounds like you'd benefit from it, let me know!