[lgessler]

Org-mode. Since it's a plaintext format it's easily searchable, and it's the most feature complete and ergonomic piece of software I've ever used for task tracking and knowledge management (including MediaWiki, TiddlyWiki, Google Docs, Evernote, plain txts, and more).

One major pain point: no totally seamless mobile sync that I'm aware of. I just write things down in Google Keep and transcribe them when I'm on my laptop next.

[LVB]

For iOS, the fairly new (~1 year old) Beorg is way better than other options I've tried, to the point of actually making Org viable for me, since I have such a dependence on mobile. https://itunes.apple.com/us/app/beorg/id1238649962

[Jaepa]

For Android systems there is Orgzly. http://www.orgzly.com/

For iOS another possible option is Editorial. There are some script addons convert orgmode to MD ↔ ORG. This is incredibly hacky though, and I'm unsure how it works.

I use beorg but it still needs a lot of work to be what I'm looking for honestly.

[Arkanosis]

Not a perfect solution for everyone as you need a computer to be always on (eg. a server, a NAS, whatever) for sync, but I've been using Orgzly on Android with Syncthing to handle the sync between all my computers and my phone, and it's much better that everything I've tried before.

[kqr]

That's my setup too and it has worked so well that I sometimes feel like I have to double check that it's still working because it runs so smoothly.

Occasionally I have to consolidate multiple edits with ediff-files, but that's normally only after I have accidentally disabled wifi on the phone for longer periods of time.

[palmy]

Just to add to this, if you take a lot of mathematics notes, you can embed latex fragments in Org-mode. Making use of the yasnippet package, writing latex is actually quite efficient.

On top of this, if you read a fair bit of papers, check out org-ref [1]. Referencing and notetaking of papers becomes a breeze.

Finally, you can also export your notes to a bunch of different formats (e.g. html, pdf).

[1] https://github.com/jkitchin/org-ref

[_emacsomancer_]

Also check out the Emacs packages interleave or org-noter (they have similar functionality): they give you a good way of taking notes on pdfs (linking the notes to positions within the pdf).

[minikomi]

I use termux, along with dropbox and dropsync, to keep my org folder synced. It required me customizing a lot of evil-mode commands to use the basic android keyboard, but it's working out great now. Heavy leveraging of org-mode templates is key.

[d0mine]

MobileOrg (+dropbox) works for me http://mobileorg.github.io/documentation/