MG4J (Managing Gigabytes for Java) is a free full-text search engine for large document collections written in Java. With release 1.1, MG4J becomes a highly customisable, high-performance, full-fledged search engine providing state-of-the-art features (such as BM25 scoring) and new research algorithms. Release 2.0 significantly improved performance and introduced several new features. Warning: R