AI research tools, tiered

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2 tools we track in this category, with a short reason and current starting price for each. Tiers are opinions; see how we rank.

The tiers

S
Gemini Notebook (NotebookLM) · Free / via Google AI plans
Source-grounded notebooks with audio overviews; renamed from NotebookLM in July 2026.
A
Perplexity · Free / $20 mo
Answer engine with citations.

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