fancyzones is pretty good but it's more like fixed layouts that you can change to, where as i3wm and other twms let you change the layout on the fly making them a bit more flexible.

Yeah, it's a bit of a push versus pull distinction: Fancy Zones sets up "zones" on the monitor that you can push applications into. A tiling window manager pulls new windows as they appear into non-overlapping "tiles". With Fancy Zones a window typically overlaps by default (just as the Windows default has been since sometime in Windows 2) until you the user pushes that window into one of the zones (using the mouse or a keyboard shortcut). A tiling window manager should default to that automatically without user intervention.

There's definitely plenty of overlap: Fancy Zones has some options to try to automatically remember to snap applications to given zones.

> push versus pull

Thanks that really clarifies how to view the projects actually.

> The subtractive Grid model starts with a three column grid and allows zones to be created by splitting and merging zones, resizing the gutter between zones as desired.

i3wm is basically like that except ad-hoc instead of preconfigured, and starting from a single full-screen window.