MCC-LIDAR is a command-line tool for processing discrete-return LIDAR data in forested environments. It classifies data points as ground or non-ground using the Multiscale Curvature Classification algorithm by Evans and Hudak:
Evans, Jeffrey S.; Hudak, Andrew T. 2007. A multiscale curvature algorithm for classifying discrete return LiDAR in forested environments. Geoscience and Remote Sensing. 45(4): 1029-1038.
The current version is version 2.1. It can be installed and will run on Windows, Linux, or Mac OS.
How to Run the MCC-LiDAR program.