Fast and multi-threaded implementation of Isolation Forest (a.k.a. iForest) and variations of it such as Extended Isolation Forest (EIF), Split-Criterion iForest (SCiForest), Fair-Cut Forest (FCF), Robust Random-Cut Forest (RRCF), and other customizable variants, aimed at outlier/anomaly detection plus additions for imputation of missing values, distance/similarity calculation between observations, and handling of categorical data.