The Flint Database Backend
Flint is a "next generation" database backend for Xapian. It takes lessons learned from studying Quartz in action, and is substantially faster (both when indexing and searching), more compact, and better in other ways too (for example, Flint uses a different locking strategy such that locks are automatically released if an indexing process exits uncleanly).
Geologically, Flint is similar to Quartz, but more useful for making tools - so the name seemed apt. It's also more one letter shorter, reflecting the improved compactness!
Flint is the default backend from 1.0.0 onwards. It was present in some form in 0.9.x too, but not the default (and 0.9.x flint databases unfortunately aren't compatible with 1.0.0).
You can use "xapian-compact" to compact and merge flint databases like quartzcompact does for quartz ones. "xapian-check" is equivalent to quartzcheck. "xapian-inspect" is roughly equivalent to an interactive version of quartzdump.