GoodRelations E-Commerce Vocabulary
OWL ontology for e-commerce: products, offers, prices, stores. Largely integrated into Schema.org.
Visit WebsiteBrowse the tree, filter it, or click any class to see just its corner of it.
Where this one tends to earn its keep.
Rich product data for search engines
Price comparison service backends
E-commerce catalog linked data
Product offer structured markup
I haven't checked this label against the actual licence text — it's the catalogue's original guess. Check the ontology's own site before you rely on it.
Others worth a look in Web Standards.