There are various open-source utilities available, depending on your platform.
Java
DAVExplorer http://www.ics.uci.edu/~webdav/
DAVExplorer is a Java-based GUI that allows you to navigate a WebDAV file system and upload and download files from it.
Linux
Nautilus
A graphical shell for GNOME. View WebDAV folder content, drag-and-drop files to and from the desktop for editing.
DAVfs http://sourceforge.net/projects/dav/
davfs is a Linux file system driver that allows you to mount a WebDAV server as a disk drive.