If percol is based on aut-fu, then it's probably not that good. The screenshot shows auto-fu, I know that zsh-plugin, but it's really messy and does very aggressive auto-completion (erasing your previous input).
I'd rather use fish-shell instead.
no percol is not shell plugin, but a simple cmdline util used in a pipeline, I suggest you take a look. I understand that animation on the website is a little bit confusing though.
