If you don't care about proprietary OS and want something that follows the Apple HIG, as well as working across Apple platforms, NotePlan is also worth a look.

If you don't care about proprietary OS and want something that follows the Apple HIG, as well as working across Apple platforms, NotePlan is also worth a look. it might look like a task manager at first, but it actually has very solid note taking / backlinking / Zettelkasten abilities. it also has a really approachable/hackable JavaScript plugin api (that works on iOS!) which is not obvious on first look.