FID4.1 is a freeware software tool for supervised classification, using fuzzy decision tree and forest. It is loosely based on the ID3 decision tree algorithm. It handles nominal, continuous, and linguistic attributes and classes. It can also operate with noisy and unknown features, both in training and testing data. For continuous attributes that are not partitioned into fuzzy sets, the system generates fuzzy partitioning using topdown and bottom-up methods. Finally, FID uses a number of inferences, falling into two classes: set-based and exemplar-based. In this paper we overview the major features and functionalities of FID4.1.