user30732: Is Ethereum open source? 
I've heard different things from different people. 
Stephan Tual has written: 
"Everything at Ethereum, including our website, our tools, our whitepapers and of course our all of our software and compilers are 100%, wall to wall open source and under the GPL."
But then what about the Ethereum Foundation? 
How does the open-sourceiodicity of Ethereum compare to that of Bitcoin? How does it compare to that of the proposed "private blockchain" Hyperledger project? 

user6441: 
Is Ethereum open source?

Yes. You can find all the source code on Github.
Technically, Ethereum - as in the idea - is open source since you can read the full specification in the yellow paper. 
Ethereum - as in the software - is open source and you can find all major and minor implementations on Github: geth, mist, etc. (GPL, LGPL)

But then what about the Ethereum Foundation?

Yes. You can find a general statement here

30732: <p>Is Ethereum open source? </p>

<p>I've heard different things from different people. </p>

<p>Stephan Tual <a href="https://www.quora.com/Is-Ethereum-open-source" rel="nofollow noreferrer">has written</a>: </p>

<p>"<em>Everything at Ethereum, including our website, our tools, our whitepapers and of course our all of our software and compilers are 100%, wall to wall open source and under the GPL.</em>"</p>

<p>But then what about the <a href="https://www.ethereum.org/foundation" rel="nofollow noreferrer">Ethereum Foundation</a>? </p>

<p>How does the <em>open-sourceiodicity</em> of Ethereum compare to that of Bitcoin? How does it compare to that of the proposed "private blockchain" Hyperledger project? </p>
 6441: <blockquote>
  <p>Is Ethereum open source?</p>
</blockquote>

<p>Yes. You can find all the source code on <a href="https://github.com/ethereum" rel="nofollow noreferrer">Github</a>.</p>

<p>Technically, Ethereum - as in the <em>idea</em> - is open source since you can read the full specification in the <a href="https://github.com/ethereum/yellowpaper" rel="nofollow noreferrer">yellow paper</a>. </p>

<p>Ethereum - as in the software - is open source and you can find all major and minor implementations on Github: <a href="https://github.com/ethereum/go-ethereum" rel="nofollow noreferrer">geth</a>, <a href="https://github.com/ethereum/mist" rel="nofollow noreferrer">mist</a>, etc. (GPL, LGPL)</p>

<blockquote>
  <p>But then what about the Ethereum Foundation?</p>
</blockquote>

<p>Yes. You can find a general statement <a href="https://github.com/ethereum/wiki/wiki/Licensing" rel="nofollow noreferrer">here</a></p>
