Swarm stores trees as plain GEDCOM 5.5.1 files on your Mac — no account, no cloud, no telemetry — and names the exact relationship between any two people, down to “second cousin once removed” or the Russian in-law terms свёкор and деверь that English doesn’t bother distinguishing. It ships an offline gazetteer of 476,958 places, plus six example trees — Curies, Darwins, Kennedys, Romanovs, Roosevelts, Tudors — to explore first. It’s free and GPL-3.0, but unsigned, so first launch needs a trip through System Settings to approve it.