Radars and blips
A blip is anything you want out of your head. A radar holds the blips about one thing, and each blip moves from Inbox to Active, Later, Done or Dropped.
There is one always-focused box and nothing to choose before you type. A #hashtag becomes a tag, a bare URL becomes a link with a preview, a long piece of writing becomes an essay, and a dropped or pasted file becomes an attachment.
Make as many radars as you like. Each has its own color, glyph and template: a stream, a Kanban board, a microblog, a reading list or a decision log.
Follow a tag to every blip that carries it, from every radar at once, then save that view as a smart radar: a radar that holds nothing of its own and gathers what matches from everywhere.