There are no categories, no contexts, no markers, no due dates...
I'm not sure what makes this is a "system". What's odd is that the author seems to have had previous incarnations/systems, that were actually more complex, e.g. had separate lists with review periods, curation, etc., but he seems to have evolved (which I really appreciate continual improvement) to "fuck it, just use one list".
I know I'm committing an error of logic, but his FVP stats seem to indicate he's basically retired/in a low stress environment [2], so perhaps all the regalia of GTD (which fwiw I don't practice) are more applicable in the corporate environments that spawned it.
However, if it works for you, that's great. It's been awhile since I've poked around in the "productivity system" space. Interesting stuff.
[1]: http://markforster.squarespace.com/blog/2015/5/21/the-final-...
[2]: http://markforster.squarespace.com/blog/2015/5/27/a-day-with...