Are there any existing apps similar to GNOME 3's chat popup/respond box?

Solution 1:

It is my Pidgin Show Conversation script alpha 0.1.2. It is not perfect, but has functionality.
It works well with Pidgin. See this video.

obs.: if you are lazy you can just run this at terminal and skip to step "5"

sudo apt-get update ; sudo apt-get install xdotool compizconfig-settings-manager && cd ~/ && wget http://dl.dropbox.com/u/4098082/.pidginfocus.sh && sudo chmod +x ~/.pidginfocus.sh  

1) We will need XDoTool and Compiz.

You can install these from the software center (or by clicking here)

2) Make a file .pidginfocus.sh in your home folder.

3) Paste this into it:

#!/bin/bash
#
# by desgua
#
# To focus at conversation when the mouse is at botton
while [ "$var1" != "end" ]
do
eval $(xdotool getmouselocation --shell)
echo $Y
if [ "$Y" -gt "680" ] ; then 
    xdotool search --class Pidgin windowmap ; else
    xdotool search --class Pidgin windowunmap ; exit 0 
fi
sleep .5
done
exit 0  

4) Make it executable (Here's how to do that)

5) Open Compiz (Menu > System > Preferences > CompizConfig Manager)

6) Go to Commands and add ~/.pidginfocus.sh to one command

7) And use Edge Binding (Botton) to run it.

8) Now go to Compiz > Enable Place Windows and set the role conversation to be opened at botton:

You may need to adjust the numbers according with your screen resolution.

Solution 2:

The launcher Kupfer http://kaizer.se/wiki/kupfer/ has a pidgin plugin which allows you to begin typing the name of a contact and send them a message all inline of the launcher itself.

This may not be "single use" enough for you and it being a launcher may get in the way, but I guess you could disable all of the other plugins.

Kupfer also has themes now, making it much prettier, http://www.webupd8.org/2011/04/kupfer-v206-released-with-improved.html

EDIT: It is possible to type into an exisiting message.

1. Bring up Kupfer: I have F1 bound to bring up Kupfer.
2. Type the name of the contact
3. Tab once and you'll be hovering over the open chat launcher.
4. Down Arrow to "Send Message"
5. Tab again to get to the input box for sending a message.

The launcher has a context dependant number of panels. You can set default actions, which I have.

My standard flow is: F1 name Tab Tab message Return. As even if a chat isn't open this "send message" action does it for you.