Offline Sorter (OFS) version 3 is a powerful, easy-to-use tool for viewing and classifying action potential waveforms (spikes) collected from single electrodes, stereotrodes, and tetrodes. Spikes can be displayed as points in either 2D or 3D feature space, where a variety of manual, semi-automated, or fully automated clustering techniques can be applied in order to classify (sort) the spikes. OFS can also perform spike extraction on continuously-recorded neural data using a variety of different thresholding methods. OFS allows verification of sorting through a variety of displays, and can calculate cluster separation statistics and sort quality metrics. The sorted spikes can be exported in several formats for subsequent analysis.