A sort of similar effect can be achieved with iTerm's hotkey window.
I usually run an emacsclient inside tmux inside the hotkey window, with a scratch text-mode buffer active.
If I want to use emacs to work on some text from a non-emacs app, the steps are something like: select text, cmd-c, press hotkey (mine is option+space), ctrl-y, edit the text, select what I need, opt-w, press hotkey to switch back to the app, then cmd-v.
Since the hotkey window is running tmux, it's easy to create or switch to another tmux window and operate on the text with the help of pbpaste/pbcopy and good old pipe.
I usually run an emacsclient inside tmux inside the hotkey window, with a scratch text-mode buffer active.
If I want to use emacs to work on some text from a non-emacs app, the steps are something like: select text, cmd-c, press hotkey (mine is option+space), ctrl-y, edit the text, select what I need, opt-w, press hotkey to switch back to the app, then cmd-v.
Since the hotkey window is running tmux, it's easy to create or switch to another tmux window and operate on the text with the help of pbpaste/pbcopy and good old pipe.