However, I believe they are fully within the licensing of wbfs (which is GPL, I believe) by offering any modifications they've made to Kwiirk's source. They do not have to release their own code, just the modifications to the wbfs libraries or command. I'm not sure if GPL requires a derivative work to include credit to the original code in their app, but it's a nice thing to do anyway.
I feel compelled to add that I have nothing against them and am not trying to start a jihad. In fact, I have switch over to the app from using the terminal and appreciate the aesthetics. Clearly the authors are talented.
However, I was wrong -- there is nothing ambiguous about kwiirk's licensing.
wbfs.c said:
// Copyright 2009 Kwiirk
// Licensed under the terms of the GNU GPL, version 2
//
http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt
So! §3
QUOTE(the terms of the GNU GPL, version 2)
3. You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also do one of the following:
a) Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of Sections
1 and 2 above on a medium customarily used for software interchange; or,
b) Accompany it with a written offer, valid for at least three
years, to give any third party, for a charge no more than your
cost of physically performing source distribution, a complete
machine-readable copy of the corresponding source code, to be
distributed under the terms of Sections 1 and 2 above on a medium
customarily used for software interchange; or,
c) Accompany it with the information you received as to the offer
to distribute corresponding source code. (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form with such
an offer, in accord with Subsection b above.)