XTF
XTF from the California Digital Library: “The CDL eXtensible Text Framework (XTF) is a flexible indexing and query tool that supports searching across collections of heterogeneous data and presents results in a highly configurable manner.”
XTF Experimental Features covers FRBR: “To implement FRBR in XTF, we chose to adapt the standard FRBR Work Set Algorithm to our purposes. In particular, we changed the method to dynamically determine work groups, rather than making this determination at index time. This allowed us to play with and tweak the algorithm without having to re-index the entire test collection (over 10 million records).”