So basically if you're a part of a network and looking for a way to edit a document (in simple text format) with multiple users without having to lock it... then Gobby is a cross-platform ready, free application that can do, just that!.
Although don't hope it to be an advanced or a fully featured text editor since it's purpose is to let you create a basic document that can be proof-read later. It's designed using the GTK+ toolkit yet integrates with GNU/Linux, MS Windows and Mac OSX platforms quite well too.
*. Comes with a simple UI.
*. Connect/Disconnect with other networks using different ports, user authentications, create a session or simply open your previously used session.
*. As said it's a basic text editor but lets you do things like: Find and replace text, go to lines, enable/disable automated indention, change font related settings (size, bold, etc) ...
... although most of these feature will have to be accessed via the "Preferences" window using the menu which is not the most efficient way to do that and could be the only complaint here (or perhaps it's more oriented around computer programmers).
*. You can start a text file from scratch or can open an existing one.
*. Syntax highlighting for various programming languages: C/C++, Java, HTML, XML, Perl, Prolog, etc.
*. Text wrapping.
*. Automatic recognition of various programming language related file extensions.
*. Send live messages.
*. Show/Hide connected users or document lists... are among its main features to mention.
You can install Gobby in Ubuntu 11.04 Natty Narwhal, 11.10, 10.10 and 10.04 by using the below command in your Terminal window.
sudo apt-get install gobbyAnyhow, if you're looking for a free text editor that supports collaborative editing + can be used on Ubuntu (GNU/Linux in general) and other OS platforms, but can cope with the fact that perhaps it's more of A programmer friendly (concerning the fact that font changing, etc type usual settings are hard to access) one, then Gobby is a pretty simple yet an effective opensource "solution" nonetheless.