Recoll is a free, open-source full-text search tool based on Xapian that helps users locate documents across their computers. It supports numerous file formats, offers both graphical and web interfaces, and works on Unix, Linux, Windows, and macOS.
BM25 is a probabilistic weighting scheme used by Xapian that combines previous models (BM11 and BM15) with a scaling factor to improve term weighting in information retrieval. Recent TREC tests have shown it to be the best known probabilistic weighting scheme, with default parameters of k1=1, k2=0, k3=1, and b=0.5 that can be tuned for specific collections and query types.