There is no readme, so here is the fast description:

Enter a URL in the text field, with the protocol part (ie: http://, or ftp://). It'll mirror it under ~/Library/WGet/[the all path to what you are downloading]

If you interrupt the mirror, it'll take (more or less) from where he left. Use man less to learn more

You can save the 'wget' documents, if you want to mirror several places. (Useless, but it is an example)

If you kill the app (from the process viewer), it will not kill the underlying wget's. You'll have to do that by hand.

Very simple things it shows:

• How to use a NSDocument application
• A way to wrap a command line with an GUI
• Async wait for data from a subprocess
• Append to the NSText object (in a complex way. Could be done simpler)