"Tabs" in Curio
I'm just starting to explore Curio, but it does seem to have the functional equivalent of OneNote tabs. It looks like there are a couple of ways to do this - you can use a new "Project" as the equivalent of a OneNote Notebook (the tab on the left side of the page), a Section as the OneNote section (the top tabs), and Idea Spaces as the pages (the right hand tabs, which in Curio can even be subdivided), that's one way to do it. Or, you can have, within one project, the Sections for the Notebooks (left tabs), Folders for the Sections (top tabs), and individual Idea Spaces for the pages (right tabs).
I like the elegance of the OneNote tabs as a quick way to navigate, and Curio's layout doesn't have that same clean feel, but the functionality is there and is the same. Since Curio seems to do everything else the same a OneNote, at least in version 7, including text anywhere on the page, etc., it looks like a good replacement. Admittedly, I'm new to both programs and still exploring, but so far it seems to work.
You can get a 60-day extended trial license for Curio 7, which should give you plenty of time to check it out, for those who are interested in trying it out.
Les