I personally use nvALT bookmarks with keyboard shortcuts Cmd-1~4 for quick access. Terrifically fast, though it lacks the multi-notes view.

I use this in my .vimrc:

" Quad-Split:
:nmap <f4> :tabe 1.md<cr><c-w>s<c-w>v<c-w><down><c-w>v:e 3.md<cr><c-w><right>:e 4.md<cr><c-w><up>:e 2.md<cr><c-w><left>

" switch between windows with SHIFT/LEFT, SHIFT/RIGHT:
nmap <s-right> <c-w>w
nmap <s-left> <c-w>W

When I press F4 I get a new tab with four windows, containing the files 1.md, 2.md. 3.md, 4.md. Shift-left/right lets me quickly change between windows. The regular vim shortcuts for this (<c-w><left> etc.) are too hard to type for my taste.

Scrivener Cork Board for Note Taking.

It'd be a wast to only use Scrivener for the cork board feature, but it works very well, and you can tab between index cards: http://www.simplyscrivener....

5iler was my immediate reaction too... :+)

have you tried 5iler (https://5iler.com) yet?

I had the same need recently and did not find any tools in my preliminary searching. Sticking with pen and paper for now.

I'd happily pay $15-25 for an OS X app. My eventual endpoint would be a single compiled entry in Day One. Bonus feature: entry title and scriptable tags pulled automatically from my calendar appointments.

Having multiple workspace configurations would be great, too. I'd probably have different workspaces for work meetings (personal notes), mentoring/consulting conversations (where I'm usually sending a report afterward), and one for lecture/learning/study.