Oni is a great GUI on top of neovim: https://github.com/onivim/oni
This project is built on top of the neovim API and adds cool modern elements: keyboard-centric file tree, VCS integration… hard to emulate clearly within the limitation of a cell-based terminal.
The “problem” with the current version is that it’s an Electron app. This platform is sadly famous for its high memory consumption and suboptimal performance in some case. (I personally found that VsCode works decently on recent machine)
So for their future version, the team behind Oni is experimenting with a new rendering engine based on a combo of WebGL and ReasonML. https://github.com/bryphe/revery
The README on the Revery’s repo explains the motivations better than I could.
I share this project here because it could turn to be a possible candidate to implement a similar Kakoune GUI in the future.