The Neural Data Simulator (NDS) is an open-source Python package designed to simplify the development of Brain-Computer Interfaces (BCIs). NDS generates real-time electrophysiology data from behavioral data, such as cursor movement and arm kinematics, replacing the BCI-user in the loop during development. This package is highly flexible, fully customizable, and comes with a set of utilities and examples that enable rapid kickstarting of BCI development. It includes pre-trained models, such as an encoder that converts behavioral data to simulated intracortical array data, decoder models, and example BCI GUI/tasks.