BobArning's browser (BobsBrowser) is an experimental code browser featuring a central code pane with various ancillary windows/menus for navigation. One key feature is the use of hierarchical lists for delving into classes/methods/etc. The current version (as of 01-Nov-03) seems to be at http://www.charm.net/~arning/BobsBrowser.14Apr1206pm.cs.txt.
Whisker is a different sort of browser, which uses Bob's collapsible hierachical list for viewing multiple classes and methods simultaneously. I've just checked out a preliminary version which looks very promising. Look here for it: http://www.mindspring.com/~dway/smalltalk/whisker.html
Dynamic context menus were done (though not in Squeak) by "Francisco J Vives"
Morphic Wrappers also known as MathMorphs, let any old object wear a MorphicSpaceSuit and then you can just splat it on the world and tell it to do things. Careful, they sometimes talk back. Class-specific MorphSuits (hey, this could be a good name for MWs...) provide an alternative to browsers.