You can get something similar to that with the Firefox vimperator plugin. Press ctrl-I in a textarea and a vim pops up. When you close it the text gets copied back. I use it a lot!
that is one of the best things in pentadactyl as well. unfortunately it still tries to use gvim for me. but this can surely be changed somehow.
set editor=(command line here), if you were curious. I've found you can easily check if an option for something exists by using :set and its nice autocompletion.
so, the links provided on that page don't work. There's a sourceforge project by that name, with some ancient code that won't work in Chrome... do you have a link to a version / repo of that that works in modern browsers?