It looks pretty open to me. However, I don't speak legalese, so I may be misunderstanding it.
https://twitter.com/shit_hn_says/status/463711610172088320
The legalese is translated into bullet points in the right-hand column.
>Today, we're excited to announce that we are open-sourcing Atom under the MIT License
It looks pretty open to me. However, I don't speak legalese, so I may be misunderstanding it.