[cagey]

> Technologically simple, was done well on MS-DOS in a few hundred kB of code and data.

Exactly. The outliner feature in Borland's Sidekick Plus was my all-time favorite, but its lifetime was brief (due to the entire product being a TSR), so I used Symantec's Grandview 2.0 sporadically over the decades, even in DOSbox out of desperation (as recently as 5-6 years ago!).