Let's see. This is MIT, but 3-clause BSD is pretty much equivalent: > Copyright (c) 2013 Felix Gilcher > > MIT License > > Permission is hereby gra

Let's see. This is MIT, but 3-clause BSD is pretty much equivalent: > Copyright (c) 2013 Felix Gilcher > > MIT License > > Permission is hereby granted, free of charge, to any person obtaining > a copy of this software and associated documentation files (the > "Software"), to deal in the Software without restriction, including > without limitation the rights to use, copy, modify, merge, publish, > distribute, sublicense, and/or sell copies of the Software, and to > permit persons to whom the Software is furnished to do so, subject to > the following conditions: > > The above copyright notice and this permission notice shall be > included in all copies or substantial portions of the Software. > > THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, > EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF > MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND > NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE > LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION > OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION > WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. The important part is: > to deal in the Software without restriction, including > without limitation the rights to use, copy, modify, merge, publish, > distribute, sublicense, and/or sell copies of the Software, and to > permit persons to whom the Software is furnished to do so, subject to > the following conditions: All I need to do is retain the copyright notice, but only if I use substantial portions. So as long as I retain the notice, stating that some specified part of the code is licensed under MIT, I'm in the clear. The permission to sub-licence is explicitly granted, no further restriction is placed on the combined work. I don't have to provide the source code either. The end result can be whatever I choose, the license does not spread to the combined work. WTFPL is even more liberal: > DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE > Version 2, December 2004 > > Copyright (C) 2004 Sam Hocevar <sam@hocevar.net> > > Everyone is permitted to copy and distribute verbatim or modified > copies of this license document, and changing it is allowed as long > as the name is changed. > > DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE > TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION > > 0. You just DO WHAT THE FUCK YOU WANT TO. No restrictions at all - effectively placing the code in the public domain, but a valid copyright waiver in jurisdictions where code cannot be placed in the public domain (e.g. in Germany, where copyrights cannot be waived)