I don't get it as well, everything mentioned in the readme is already trivially possible with tmux or zellij

windows support + async + public sdk. You can rewrite zellij with rmux, but not the opposite. rmux is a multiplexer engine

rmux is much faster than tmux or zellj, I did some internal benchmark and it's promising. rmux is a multiplexer engine, meaning that you can rewrite entirely zellij using rmux.. I created a mini zellij in a few hundred lines of rust. You can check the demoes on the repo

But wait, I’m a user of tmux or zellij which for me was basically another tmux and I went back to tmux eventually. I’m not looking to develop another tmux or something. Is this project more of a library to create tmux like apps?

As of today you can replace tmux by rmux. Its behavior should be 1-1 iso; tmux is more stable though, it has been battle tested with a dozen of years of edge cases refinement. rmux is a faster and more elegant clone of tmux + windows support + programmable sdk

I mean, the obvious immediate answer is “windows”, which tmux flat out doesn't support (except via WSL and a shared mount).