The core is open-source and available on GitHub [1], but seems to be scattered across a number of repositories. Not clear if it's buildable purely from the repository currently (I haven't tried).

It was previously an independent open-source project, AndroVM [2], which Genymobile acquired, but they agreed to keep the core open-source [3].

[1] https://github.com/androvm

[2] http://androvm.org/

[3] http://androvm.org/blog/blog/2013/05/16/androvm-moving-to-a-...