Google Knowledge Graph
Google's proprietary knowledge graph powering Knowledge Panels in search. Read-only API available.
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.
Enrich search results with entity data
Power knowledge panels and rich snippets
Entity understanding in search queries
Build on Google's entity recognition API
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 Knowledge Graphs.