I’m a big Curio fan myself. I’ve used Notetaker 4 and agree that it might be the most similar product to CPN on the market. Here’s a previous MPU discussion of Notetaker 4. I’m hoping there’ll be a Notetaker 5.
I think one thing to keep in mind is that Notetaker 4 is currently $29.99 and many competing products are priced higher.