The C++-based ROot Workflow for N-tuples (CROWN) framework is a fast way, of converting CMS NanoAOD samples into analysis N-tuples.
Installing the framework is easy (not much more than a git clone), check the Installation Guide
A small introduction on how to run the framework can be found in this Running the framework Guide
The full documentation can be found at https://crown.readthedocs.io/en/latest/.