I’m a very long time user of OmniOutliner and unlikely to switch to anything else - however, my eye has recently been caught by ‘outlinely’ which seems to have a lot of fans. what attracted me was that it has a minimalist look and feel somewhat similar to Ulysses, of which I’m an avid user.
I note that outlinely, like ulysses, features a unified library, in the form of a collapsible sidebar containing access to all of the app’s documents.
I think this would be a really helpful feature for OO, and I wonder if anyone else agrees with me. I haven’t yet submitted a feature request for this, but I will if there’s some interest here.