How to (and who can) implement the standard library features defined by the C++ committee?

When the C++ committee publish a new feature that will be part of the standard library in the next standard of the language, they also release some source code or some kind of guidance on how to implement that feature?

Let's take unique_ptr as an example. The language committee just defines an interface for that class template and let the compiler vendor implement it as it wants? How exactly this process of implementation of the standard library features occurs.

Can anyone implement parts of the standard library for a platform that doesn't have support for it yet? Let say I would like to implement some cool features of the C++ standard library to use it on a microcontroller environment. How could I do that? Where should I look for information? If I decide to turn my project open source, can I do that? Will I need to follow exactly what the standard say or I can write a non-compliant version?