I think Kakoune is particularly interesting here because it integrates window splitting using tmux and a client-server model instead of re-implementing it which is what vim does. This is part of Kakoune's design philosophy: to be composable with other unix tools. Other examples of this are file browsing[1] and fuzzy finding[2] using ranger and fzf, or even just piping a selection to `fmt` to reformat a paragraph.

[1] https://github.com/mawww/kakoune/wiki/Ranger

[2] https://github.com/mawww/kakoune/wiki/Fuzzy-finder