NotebookLM did something useful: it made "an AI that only answers from the documents you give it" a normal thing to expect. Since then a lot of tools have shipped some version of the same idea, and if you're looking for an alternative, the hard part is that most of them describe themselves in nearly identical language.
Here's what actually varies between them.
What they mostly agree on
Almost every tool in this space now does the core thing. You add PDFs, docs, or links, and you ask questions that get answered from that material with citations back to the source. Open Notebook, AnythingLLM, ChatGPT Projects with a "use only these sources" instruction, and several others all cover this. If that's all you need, the choice comes down to price, file limits, and whether you want it running locally or in the cloud.
That baseline is no longer the thing that separates tools. It's the price of entry.
The questions that separate them
Can it work across everything at once, or one notebook at a time? NotebookLM keeps each notebook separate, and you can't ask a question that spans two of them. For a project with material in more than one place, that's a real limit, and some alternatives are built specifically around removing it.
Does it just retrieve, or does it also push back? NotebookLM is strong at pulling the exact passage and weaker at arguing with it. ChatGPT and Claude are the reverse. A few tools are trying to do both: accurate citation plus the ability to challenge what a source claims or point out where two sources disagree.
Where does the answer live once you have it? Most of these tools are a question box. You ask, you read the answer, you copy the useful part somewhere else. If the work is synthesis, tying several sources together into something of your own, a plain chat log is a poor container for it.
Can you tell when it doesn't know? The tools worth keeping say "the sources don't cover this" instead of filling the gap with a plausible answer. Test this directly: ask something your documents clearly don't address and see what happens.
Where Graphia fits
Graphia is in this category but built around a different shape. Instead of a notebook and a chat box, it's a canvas. You drop in your documents and links, write your own notes directly next to them, and the AI reads the whole surface at once. It answers from your material with the source attached, it works across everything rather than one notebook at a time, and it can organize and edit cards on the canvas, not only reply in chat.
If you're comparing options under the "NotebookLM alternative" label, the useful test isn't whether a tool cites its sources. They all do now. It's whether the tool is a place to think with your material or just a place to query it.