CrossLine – outliner with sophisticated cross-link capabilities like Ecco Pro

Careful, Herr Keller: I know of at least one Ecco Pro person who was so enamoured of cross-linking that they fell down the Xanadu rabbit hole :-)

(or maybe you should fall down it? Despite the promise of the early web, we're just barely into the era of transquotation: https://en.wikipedia.org/wiki/Transclusion#:~:text=an%20expl... )