I believe that is what is being shown. The tool is (I think) being demonstrated in a zshell with that feature (and probabaly countless others) turned on, so it is difficult to tell what is shell and what is percol. Or maybe not. The point is I don't know.
I worked on a similar project: a tool that (primarily) tees it's stdin to your tty before you decide how to continue your pipe[1], which is a little more general, though it's admittedly less polished or nice. I think there's an interesting space in making the process of writing commands more interactive, though doing that really well will involve an intelligent solution to the problem of commands with side effects.
It's just a good idea that was never (AFAIK) done for shell only interactions. Often good to be able to have progressive enhancement (people not allowed to install emacs say).
Would you mind sharing what that alias would look like and do? I can only imagine it appending the string "| tmenu" to the current line, eventually pressing Return for the user as well.
Warning: seems like GNU readline isn't case sensitive so C-L === C-l thus, in this example, C-l default behavior (clear screen?) is overridden. I didn't RTFM so trust yourself.
Note that most likely git.el is not on your load-path. After it is loaded, you can use M-x git-status to interactively stage, diff and commit files. In the git-status buffer you can checkout a branch with C-c C-o. If helm is installed, you'll get something similar to percol right in Emacs.
The gif animation is confusing to me because the shell appears to be extensively customized, so I can't tell what is percol and what is crazy zshell customization.
