These guys make the hardware that $VENDOR rebrands and sells as an appliance.
In short, No.
The text editor in Gnote or Tomboy looks similar and works sorta like Onenote, but that's where the similarities end.
Onenote automagically OCRs screenshots into searchable text. The ability to add any attachment is entirely too useful.
I work with technical documents that are almost entirely delivered in pdf. PDF is such a shitty format for actual reading. It's like marketing runs the engineering and technical writing departments. Print to OneNote helps with this quite a bit, especially the OCR part. As an aside, I do most reading on an e-ink device anymore and just convert the pdf's to mobipocket format -- it works about as well as you'd expect, so I'll occasionally have to reference the original. I do most of my note taking on the ereader and then upload those notes back into Onenote along with the original pdf.
As some of the other posters have indicated, you can use the mic on you're laptop while note taking to record the lecture audio, Onenote is supposedly even able to convert that to text as well, but I've not tried much.
I don't get some of the other posts about using equation editors. Paper and pencil is still a far superior medium for this. Plus anyone taking notes in a math class is mostly missing the point.
Until about three months ago, I used to take all of my notes with a text editor and screenshots. I used the filesystem to organize my screenshots, pdfs and notes together. It turned out to be far more efficient to just use OneNote, plus I can search _everything__too.