FoldingText is a very intelligent plaintext editor for the Mac. It understands the document structure and allows you to fold sections and even focus sections to work on (like an outliner). It understands a flavour of Markdown and lets you create Todos and Timers within the same document.
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Looks interesting. I use Workflowy (http://workflowy.com) for a lot of the use cases - outlines, folding text in long notes, todo lists, etc.
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ya it looks like a non-cloud version of workflowy. Personally I prefer workflowy
Framer