Zellij
Terminal multiplexer written in Rust, first released in 2021 (originally called Mosaic). tmux, but discoverable — the keybindings are printed along the bottom of the screen.
It differs from tmux in three ways: a status bar that shows the available modes instead of expecting you to memorize Ctrl-b prefixes, layouts declared in KDL files that bring up an entire workspace in one command, and a plugin system built on WebAssembly (plugins can be written in any language that compiles to Wasm). It has floating panes and session sharing. Heavier on memory than tmux, and it lacks twenty years of accumulated muscle memory, which is the only reason most people stay put.