A new ATG module named FileBrowser is available for download. This module allows to explore a
server's filesystem from within an ATG instance, and it's a JSP port of Will Sargent's Filebrowser module
with additional functionalities (downloading and deleting of files, revised interface).
A screenshot of the module in action, exploring my laptop's C:\WINDOWS\system32 directory (click the picture for a larger image):

Download the module, unzip it and place it into the ATG module root, start Dynamo with bin/startDynamo -m FileBrowser, and access the application at http://host:port/file-browser/.
Update: added version 1.1 with file upload functionality
A screenshot of the module in action, exploring my laptop's C:\WINDOWS\system32 directory (click the picture for a larger image):
Download the module, unzip it and place it into the ATG module root, start Dynamo with bin/startDynamo -m FileBrowser, and access the application at http://host:port/file-browser/.
Update: added version 1.1 with file upload functionality