Ecco Pro outliner. Technically it still runs on w10, but the various glitches forced me to onenote.
I also really miss my nt4 system: office 95, delphi 3, coreldraw 5, photoshop 5, netscape 4. Despite having only a 233 mhz cpu and 128 megs of RAM that system seemed more responsive and easier to use than my current pc's, and it did everything i needed it to.
Maybe Treeline[0] (a favorite of mine) or BasKet[1] (not sure if a windows version exists) suit your needs. They're both open source and more responsive than onenote.
I also really miss my nt4 system: office 95, delphi 3, coreldraw 5, photoshop 5, netscape 4. Despite having only a 233 mhz cpu and 128 megs of RAM that system seemed more responsive and easier to use than my current pc's, and it did everything i needed it to.