NotebookLM

Business and Productivity - Pricing: freemium - Editor rating: 4.0/5 - https://notebooklm.google.com

Google's research notebook - upload your documents and it answers, summarizes, and even makes a podcast from them.

NotebookLM flips the chatbot model: instead of asking a model what it knows, you upload your own sources - PDFs, notes, links, videos - and it answers strictly from them, with citations back to the exact passage. Its Audio Overview feature turns your documents into a surprisingly natural two-host podcast, which has made it a favorite for studying and briefings. Free with a Google account, with higher limits on paid plans.