Powerlevel9k was a tool for building a beautiful and highly functional CLI, customized for you. P9k had a substantial impact on CLI UX, and its legacy is now continued by P10k. [Moved to: https://github.com/Powerlevel9k/powerlevel9k]
Why do you think that https://github.com/erikw/tmux-powerline is a good alternative to powerlevel9k