The University of Glasgow recently released Terrier 2.0, just in time for ECIR 2008.
The new version has two new main features: 1) Faster and more efficient single-pass indexing and 2) A new Divergence From Randomness (DFree) retrieval model. See What's New for a complete list.
The new version has a new faster, single-pass indexing architecture from Roi Blanco from the University of Coruna in Spain. Roi is organizing the first Efficiency Issues in Information Retrieval Workshop at ECIR with Fabrizio Silvestri.
The DFree retrieval model provides a robust parameter free(!) retrieval model. In short, it should be able to be applied to new document collections without need for any tuning. It was contributed by Fondazione Ugo Bordoni, very likely including Gianni Mati.
Last year, I included Terrior in my previous roundup of open source search engines.