I feel this will work for a lot of people, especially less technical users. I have settled on Org and or Markdown, to Dropbox if required sync. Emacs and or any other text editor will just works. That said just taking notes in a consistent place and in a consistent format gets you 80% of the way there. Grep and find still work. I almost always end up back there :)
Org is its own little world, but I know that I can always edit an Org file on any computer with my preferred editor.
I like this trend of back to basics in computing (even if it is running in a web browser on my desktop), its goals are nice.
edit:nvalt is open source. Mac only and as others pointed out not updated too regular but I know people who love it.