I think it's possible to program that window with Mars :) But I also guess that from each row of the tree you can open a pop-up menu with options, right? That is not yet done, although there's some work on it already, and it was among my next steps.
Now, a further step would be to "hide" the Pharo image so the Mars application can be launched as a normal native application, but we haven't discussed about it yet :P
Esteban, your idea was to do a describe a spec of that window to build the corresponding Mars application? I think that at least the "skeleton" (plain UI) of the Pharo Launcher is simple enough for a new Mars user to do, the MarsClassesAndComments example
is a very very simple application that uses a MarsTree list, so maybe he can base the Pharo Launcher application on that one and then see how to use a MarsButton also by just looking for references of that class in other examples.
Anyway, by the end of this week I should have more documentation on how to use each widget.