Since June 2011, several major search engines have been collaborating on a new common data vocabulary called Schema.org.
The schema.org vocabulary can be used with JSON-LD, Microdata or RDFa 1.1 Lite syntax, and it has types for BreadcrumbList, Event, Organization, Person, Product, Review, AggregateRating, Offer and hundreds of others.
See schema.org releases page for the latest developments, and schema.org and FAQ for full details. The Google Search Gallery provides an overview of Google's growing set of schema.org-powered Search features.