Native Features is a powerful name for a technique and API with a simple goal: to allow the software running inside ARAnyM use certain features of the host platform. Various emulators used their own incompatible hacks but we wanted to set up something that could become a standard for other Atari emulators as well. Video, audio, network and other NatFeat based drivers should work on any NatFeat enhanced Atari emulator.
Even though the origin of the ideas are from an emulation world the Native Features are designed so that it is possible to create and use the same functionality on a real Atari machine with no changes required to the applications that use them. The key aspect is to use the appropriate operating system abstractions. Everyone is highly encouraged to read the best practices document as a basis to further attempts to use or create Native Features.
Native Features authors should see the Native Feature Development Guide to get an idea on how to properly provide a new Native Feature functionality to the Atari world. There is a complete documentation of all the provided API to create new Native Feature as well as various references to further material.
Here is the original draft about Native Features.
Here will be the list of current nfapi.
And here you'll find Native Feature Development Guide of a working NatFeat driver.