Lots of people are interested in the Daybook.
It's not immediately clear to me whether he is talking about an actual product made in/for Tinderbox, or if he is just theorizing.
Yes, it's real. And the version I described is such a simple Tinderbox document that there's not much point in distributing a prototype. Make a note for today: voila! Tomorrow, make another note. Now, make a container to hold both those notes. Perhaps sort by date. That's all you need to get started.
Of course, Tinderbox could do a lot more. How much additional work is going to be useful? We don't know yet! Jon Buscall has his own Daybook, a more elaborate system, and he's not quite sure whether the simpler version would be better or worse.