What Technolgy Ahref, SEMrush Use and how they work in the backend?

This question stricks most of the time whenever I use these sites like ahref and SEMrush, I wonder what technology they are using to make such a complex application. I would love to know if anyone can pass some knowledge about these sites working in the backend. Also, Neil Patel made his Uber suggest site not that complex but incredible app to get the keyword suggestions and other reports easily. I am hungry for such type of knowledge please share if anyone knows, How these sites works