pmenu is described as 'Terminal fuzzy finder/dmenu-replacement'. There are more than 10 alternatives to pmenu for Mac, Linux, Windows and Vim. The best alternative is fzf, which is both free and Open Source. Other great apps like pmenu are fzy (Free, Open Source), Peco (Free, Open Source), Percol (Free, Open Source) and Selecta (Free, Open Source).
fzf is a general-purpose command-line fuzzy finder. * No dependencies * Blazingly fast * The most comprehensive feature set * Flexible layout using tmux panes * Batteries included * Vim/Neovim plugin, key bindings and fuzzy auto-completion