Hello,

  I'm one of the creators of Checkvist, and this tool is worth considering regarding your needs.

  Please note, Checkvist is strongly keyboard-centric, it is supposed you can do almost everything from the keyboard.

> - Ability to hold more than 1 line of text in an item. Few desktop apps can do that, and almost none does it well. Even MLO can't, and when you're limited to one-liners, you can't really type what you're thinking. Adding notes in a separate pane is not a substitute, since you have to constantly jump between the outline and the notes pane, which kills your flow!

   You can add new line when adding an item with Shift+Enter - thus adding multiline text.
 
> - Fast instant search with filtering, just like WorkFlowy! No Ctrl+F and show a dialog box, that's so 1990s!

  You have this. Focus filtering field with '/' and start typing.

> - Virtual views, where items are filtered based on user criteria (and shown as a flat list). MLO does that.

  If you filter your list (using tags, due dates, changed: last week etc.) you can create a permalink to such filtered view, which will keep your filtering + collapse/expand state of the items. This permalink can be sent to you colleagues (you need to share your list explicitly first).

> - Keyboard shortcuts to edit/rearrange the outline structure

  Use '?' to see keyboard shortcuts - there are many. Ctrl + Up/Down/Home/End to rearrange items, Tab, Shift+Tab etc.

> - Some form of appending additional, unobtrusive notes to items.

  Use 'nn' shortcut to add notes. Also try 'aa' shortcut for more commands.

  Please write [email protected] if you have any questions.
 
  All the best,
  KIR