Right now is an interesting time for this type of program. Many people are realizing their value and adding different features. Unfortunately finding one with all the features you want is tough.
-kfitting
The downside is going to be too many similar programs all with different and incompatible file formats, so once you're committed, it will be very hard to change.
Add TreeDBNotes to the list of Keynote replacements.
Both a "lite" free version and a (presumably freely-distributable) viewer, too. That's good; I'd prefer something that was all-free, partly because of cost to me, especially if I want to have copies at home
and at work, but a free viewer would be a help if the program isn't itself free. I see Maple has that, too.
I took a look at this one and if "Novo Libero" or Neomem do not take off, I am
It looks too early to commit to either of those, especially "Novo Libero!"
which is the use of nodes as filters and make notes have properties.
I don't understand those features, which probably means I don't need them
Have you tried the SEO Note that Stefan mentioned, and if so, how does it compare with the others?
There's also a free "lite" version of Action Outline now, but it looks too "lite" to be very useful. If I read it correctly, nodes can only have up to seven child nodes. Better viewed as an unlimited-time trial, perhaps.
Really, I don't need an organiser so much as a free-text database. But those are rare, expensive, and complex.