Check out https://podfeed.ai, it's focused on the audio generation part but with more customization.

Here's one sample: https://storage.googleapis.com/podfeed-public-bkt/audio/seoul-declaration-dialogue-en.mp3

(There are a few more on the app's landing page)

Disclaimer: it's my startup. Lest anyone say I just copied NotebookLM, I started this before NotebookLM launched. The irony is that I used to work for Google until very recently and was completely blindsided by NotebookLM. But well.

Anyways, I will be the first to say that the audio quality doesn't sound as natural as NotebookLM's, but here's where I think I've done something better:

1 - More audio language options (40+ languages)

2 - More user controls: you can specify between monologue (single voice) and dialogue, length, level (NotebookLM tends to dumb everything down which is what annoys me the most), and emphasis (what to focus on). We'll be soon adding the ability to choose specific voices.

3 - The UX is entirely focused on audio generation, as opposed to being a note-taking app that does a lot of things including generating audio.

4 - We have one nice feature which is that you can add the audio to a private podcast feed we automatically generate for you, which you can add to your favorite Podcast player. We're also working on generating a shareable link.

5 - As it's typical of Google consumer products, they're probably collecting a lot of data that you put in. Google has very strong security and privacy practices, of course. But remember, if something is free, you're the product =)

Also, for what it's worth, my vision for this product is for it to help you transform any kind of content into a format that works best for you to consume. Audio is what we're starting with, but we have some ideas we're cooking. I'm also in talks with Google so that we can be one the first ones to try their newer voice models when they release them as an API commercially, and we then we'll add that to the product.

We're unfortunately unable to offer this for free (we're not Google), but we're offering a 50% discount on the first month, and you can cancel anytime. Give it a go, tell me what you think. If you think it was a complete waste of your money, reach out via the contact form and ask for a refund within the first 7 days. Just please tell us why.