Beyond the month, no specific date is provided in the announcement, but when Microsoft does open the doors, ChakraCore will be available via GitHub as a self-contained component "that can be embedded in derivative products and power applications that need scriptability such as NoSQL databases, productivity software, and game engines", according to principal program managers Gaurav Seth and Adalberto Foresti.
At that time, Microsoft will also "provide more detail on our initial priorities and guidance on how to contribute effectively to the project".
There's no mention of the license the code will be released under, but a comment over on Reddit by the company's Brian Terlson indicates it'll be the MIT license, which is certainly permissive enough that ChakraCore should see plenty of use outside of Edge.
The virtual machine is certainly no slouch, according to Microsoft's benchmarks:
I'm sure we'll get more information come January, but at this rate, Windows will be open-source by the end of 2016*.
* Joking. Maybe.