Try golgi, written by Michal Starke (Michal.Starke at lettres.unige.ch).  I had to debug it a bit, and its alpha-grade code, but it has great potential.  I'm not sure where I found it (I think on the
uiuc ftp site).  It is both a folding editor (outliner) and a code editor that knows Smalltalk syntax.  It has little rotating triangles like the Mac finder list views - click on them, they rotate and
reveal all the sub-entries beneath them.

If you need something that works out of the box, this is not it.  On the other hand, you will learn a lot about Squeak in the process of making it work (which was not too hard under 2.4).

Ed