Specify that Transmission is under GNU GPL

https://trac.transmissionbt.com/browser/trunk/COPYING
Specify that Seil is in the public domain

https://github.com/tekezo/Seil/blob/master/COPYING
Specify that Hex Fiend is under 2-clause BSD

http://ridiculousfish.com/hexfiend/files/License.txt
Specify that ImageOptim is under GNU GPL

https://imageoptim.com/
See "Open Source" section
Specify that Cyberduck is under GNU GPL

https://cyberduck.io/?l=en
See section "We are open"

Source code: https://trac.cyberduck.io