MiKTeX can be built on Windows and a subset of MiKTeX can be built on other platforms as well.

Getting MiKTeX Source Code

GitHub

MiKTeX source code is available on GitHub.

Tarball

If you prefer a compressed tar archive, you can download it here:

Date: 10/31/2016
File name: miktex-2.9-2016-10-30.tar.xz
Size: 23.6 MB
Download