Online editor

Ok, another wacky question:

I have a friend who’d like to help me out on a side project I have.
I have the side project on a server I have full control of, and it is
already using SVN (and, as I’m posting in the RoR forum/mailing list:
it’s a Rails project).

What I’m hoping exists is something that works similarly to a wiki, but
is instead a source code editor. It absolutely has to be web-based, and
has to be pretty light-weight, because he’s going to be doing most of
the work from his job, and they’re fairly restrictive about what you can
load on the PCs, although very loose about what you do while you’re
waiting for work to come up (so they won’t mind him doing the editing,
they just won’t let him download an editor to do it with).

Now, he can use a web-based SSH client that he found to log in to the
server and use something like vi or whatever: but that sucks.

I’m hoping for an IDE-ish web-based development tool he can use to
access my source (either directly on the server, or through the SVN
repository [which allows web access]).

If anyone has any leads on this, I’d really appreciate it.
If not: If someone has any suggestions with a place to start from
(taking some already available wiki-type tool and converting it into
what I want), that would also be appreciated.