Skeleton-dial watches
References in the Grail Atlas catalog carrying the skeleton complication.
A skeletonized movement has its plates and bridges hand-cut to reveal the gear train, escapement, and mainspring barrel through the dial side. Done well, it is one of the highest expressions of finishing craft. Done poorly (which is most of the time), it sacrifices legibility for a kinetic dial that reads like jewelry rather than horology.
What to look for
Audemars Piguet Royal Oak Openworked 15407 / 16204 is the integrated-bracelet skeleton at the highest production tier. Vacheron Constantin's Overseas Perpetual Calendar Ultra-Thin Skeleton 4300V is a different sort of statement. Cartier's Santos-Dumont Skeleton uses the Roman numerals themselves as bridges — a smarter dial-geometry trick than most skeletons attempt. At a more accessible tier, the H. Moser Streamliner Skeleton and Hublot Big Bang Unico Sapphire are the conversation pieces. The thing to look for is whether the openworking is hand-cut and finished (Audemars Piguet, Vacheron) or machine-cut with anglage stamped rather than applied (most of the rest). The wrist appearance differs sharply.