As we mentioned over the weekend Unity released their C# code on Github. This is not a full release, instead the code is mostly that for the editor as well as wrappers over the underlying C++ code. This release is also under a very specific and heavily restricted license. Let me say this very clearly in bold text, this is not an open source release! This instead is to help people debug what is going on behind the scenes, not for developers to extend upon or fix the underlying source code. The code is for the most current version of the editor.
Further details from the Unity developer blog:
We are not releasing Unity as open source. Not even a little bit. (Sorry.) It’s not that we don’t like open source. We’d open source all of Unity today if we thought we could get away with it and still be in business tomorrow, and we do have a growing number of open source projects. But the main engine will remain proprietary for the foreseeable future, and the C# reference source code is released under a license which only permits you to read the code, not modify it. Please consult the full license text for details before you get carried away.
We also do not take pull requests against the C# reference source code. We have neither the legal nor organizational frameworks in place to handle such PRs, not to mention that the mere act of preparing a PR is actually against the reference license (which, again, doesn’t permit modifications to the code). We would like to hear about it if you find a bug in the C# reference source code, but please report it using the Unity Bug Reporter (describing the issue and possibly linking to the relevant lines or files in the reference source code), not by submitting a pull request on GitHub.
The source code is available on Github here. For more details be sure to watch the video below.