TextEditAid

This extension allows you to edit (or just filter) the contents of a textarea on a web page. Since Chrome does not allow the running of an external program directly, this extension instead makes an ajax call to a web server, which can start up a graphical editor, or perform any kind of filtering you desire. The URL that is used is configurable in the options.

When a textarea receives the focus (e.g. if you click in one), the icon will get a click action (indicated by the mouse-over title text). When left-clicked, an ajax request will process the currently-selected textarea and update the value when the request is done (e.g. when the editor exits). You can also assign a keystroke to use to activate the editor (I like Alt-Enter), which allows you to leave the extension's icon unpinned.

Change Log:

1.0.8 - Renamed TextAid to TextEditAid & tweaked for newer chrome.
1.0.7 - Tweaked the OK/Cancel buttons on the options page.
1.0.6 - A fix for Mac OS X that made clicking on the icon not work.
1.0.5 - Include the status text in the failure alert so it is clearer what needs to be fixed.
1.0.4 - Avoid spurious failure alerts after a successful update. Added support for http basic auth (you'll need an updated version of edit-server or whatever script you're using).
1.0.3 - Added a configurable keyboard shortcut (defaults to disabled).
1.0.2 - Fixed a newly-introduced bug with the field editing.
1.0.1 - Changed event capturing method so that focusing any textarea shows the clickable icon.

The edit-server script that I wrote (in perl) for use with TextEditAid:

http://opencoder.net/edit-server

Another option are the servers written for the emacs_chrome project (the python one worked fine when last I looked at it, though it was only single-threaded). You could also supply your own server script, or run a CGI under a normal web server. See the options page for more information on the POST request used.