> This is a challenge with the iOS (and Android) UIs, I think. Mice and trackpads have a more obvious and somewhat richer set of "verbs" for interaction
GTK+3 has a good approach there, I think. It turns the window titlebar into a thick "header bar", which includes a "title" part for easy grabbing as well as a handful of button-accessible menus (fewer than the top levels in a traditional menubar), including a kitchen-sink "hamburger menu" for lesser-used options. It becomes a bit less convenient for mouse&keyboard use, but the touch usability is absolutely there. Too bad that running Linux on tablet-like computers is still way too fiddly, it could be a fierce competitor to the iPad ecosystem for more pro tasks.
Added: And on recent GTK+3 releases, one can shrink the window horizontally and the buttons will simply shift to the bottom when there's not enough room for them in the top headerbar. This solves a flexibility issue with the previous headerbar-only approach (especially on smaller or lower-res screens), while still being quite intuitive.
These aren't visual watermarks like what you'd get on physical paper. They just alter the digital copy so that it can be traced back to the buyer, and people are deterred from sharing it on the web. It's a very elegant solution if the 'watermark' can be made hard enough to remove, and I can see quite a few workable approaches.
It has hjkl, right? What more could you need?