2048 game – How it started? Interview with the author

That said, the authors of Threes! are happy to see their ideas spread and according to wikipedia are ok with the clones[2].

As for comparing the games, Threes! is much harder than 2048 and friends. I recommend checking it out if you haven't yet.

[1] http://asherv.com/threes/ [2] http://en.wikipedia.org/wiki/Threes!#cite_ref-28

...this is it, i can't take any more!