Begone, DRM! Also fixes
It seems that we've disappointed some of you by providing a not-really-DRM-free version to those who wanted it to be completely DRM-free. We want to apologize for that; it didn't occur to us that many people care about it that much. So it seems logical to fix this. We're glad to announce that the DRM-free version (i.e. the non-Steam one, the one you download directly from our servers) is now indeed absolutely DRM-free and doesn't require a key. (It's not like keys stop pirates anyway.) So if you just want your basic click-download-install routine with no third parties involved, you are now all set for it. Sorry once again, hope it wasn't too much of a stress. We would also like to add that this DRM-free version is freshly patched, so it's the best there is! You can also look through the list of fixes here.
Oh, and if some of your friends want a DRM-free copy of Knock-Knock, they can always purchase it on GOG.