Gemini Notebook
The citation-per-answer discipline makes this the rare AI research tool where you can check every claim against the page it came from, and the free tier is generous enough for real work. The catch is dependence on Google's account and plan ladder: the code sandbox and the biggest notebooks only appear once you are paying for AI Pro or Ultra.
Pros
- Answers carry inline citations back to the exact source passage
- Wide source intake: PDFs, Google Docs and Slides, web pages, YouTube, pasted text
- Audio Overview turns a source set into a listenable two-host briefing
- Usable at no cost with an ordinary Google account
Cons
- No public API, so it cannot be embedded in another product
- Newer capabilities land on paid Google AI tiers first and roll out gradually
- Prices are shown per region in local currency, which makes cost comparison awkward