• Linked Open Vocabularies
• Lists of ontologies - A short meta-list of lists of ontologies.
• Ontology List
• Protege Ontology Library - Listing 100+ ontologies.
• prefix.cc - Namespace lookup for RDF developers.
• BARTOC (Basel Register of Thesauri, Ontologies & Classifications) - Database of Knowledge Organization Systems and KOS related Registries, developed by the Basel University Library, Switzerland.
• OntologyDesignPatterns.org
• BARTOC (Basel Register of Thesauri, Ontologies & Classifications) - Database of Knowledge Organization Systems and KOS related Registries, developed by the Basel University Library, Switzerland.
• The Linked Open Data Cloud
• BioPortal - A comprehensive repository of biomedical ontologies.
• DBpedia Archivo - Ontology archive automatically indexing OWL ontologies on the web.
• Ontology List
• Linked Open Vocabularies
• KBS/Ontology Projects Worldwide - A List of 300+ ontologies and related resources, maintained by [Peter Clark](http://www.cs.utexas.edu/users/pclark/).

Upper-level Ontologies

• BFO (Basic Formal Ontology) - A small, upper level ontology that is designed for use in supporting information retrieval, analysis and integration in scientific and other domains.
• DBpedia Ontology - A shallow, cross-domain ontology, which has been manually created based on the most commonly used infoboxes within Wikipedia.
• DOLCE (Descriptive Ontology for Linguistic and Cognitive Engineering) - A foundational ontology originally developed in WonderWeb project. ([old page](https://web.archive.org/web/20180716182415/http://www.loa.istc.cnr.it/old/DOLCE.html))
• SUMO (Suggested Upper Merged Ontology)
• YAMATO (Yet Another More Advanced Top-level Ontology)
• GFO (General Formal Ontology) - A top-level ontology for conceptual modeling, which is being constantly further developed by Onto-Med.
• DBpedia Ontology - A shallow, cross-domain ontology, which has been manually created based on the most commonly used infoboxes within Wikipedia.
• SUMO (Suggested Upper Merged Ontology)
• YAMATO (Yet Another More Advanced Top-level Ontology)

Cross-domain Ontologies

• ConceptNet - An open, multilingual knowledge graph.
• Cyc - A knowledge base which contains more than 630,000 concepts.
• DBpedia - A crowd-sourced community effort to extract structured content from the information created in various Wikimedia projects.
• KBpedia - A comprehensive knowledge structure for promoting data interoperability and knowledge-based artificial intelligence (KBAI). It combines Wikipedia, Wikidata, schema.org, DBpedia, GeoNames, OpenCyc, and UMBEL.
• Mosaic Knowledge Graphs - ATOMIC + ConceptNet combination by AllenAI.
• NELL ontology and knowledge base - An ontology developed by the Never-Ending Language Learning (NELL) project.
• Wikidata - A free and open knowledge base that can be read and edited by both humans and machines. It contains more than 55,000,000 data items.
• WordNet - A large lexical database of English. It consists of ~117,000 synsets (groups of synonyms).
• YAGO - A huge semantic knowledge base, derived from Wikipedia WordNet and GeoNames. It has knowledge of more than 10 million (10,000,000) entities.
• Xlore - A large-scale multilingual knowledge graph by structuring and integrating Chinese Wikipedia, English Wikipedia, French wikipedia, and Baidu Baike.
• Billion Triple Challenge (BTC) 2019 Dataset - A result of a large-scale RDF crawl (accepting RDF/XML, Turtle and N-Triples) conducted from 2018/12/12 until 2019/01/11 using LDspider.
• MindNet - ... by Microsoft.
• SENSUS
• Open Multilingual Wordnet - A list of open wordnets in a variety of languages, all linked to the Princeton WordNet of English (PWN).
• ConceptNet - An open, multilingual knowledge graph.
• DBpedia - A crowd-sourced community effort to extract structured content from the information created in various Wikimedia projects.
• Xlore - A large-scale multilingual knowledge graph by structuring and integrating Chinese Wikipedia, English Wikipedia, French wikipedia, and Baidu Baike.
• Billion Triple Challenge (BTC) 2019 Dataset - A result of a large-scale RDF crawl (accepting RDF/XML, Turtle and N-Triples) conducted from 2018/12/12 until 2019/01/11 using LDspider.
• KYOTO 3 Domain - An ontology which consists of ~1900 classes.

Domain Ontologies

• Gene Ontology (GO) - The world’s largest source of information on the functions of genes.
• Uberon - All body parts across all animals.
• GoodRelations - The Web vocabulary for e-commerce.
• Product Types Ontology - High-precision identifiers for product types based on Wikipedia.
• SIOC (Semantically Interlinked Online Communities) - An ontology of terms that can be used to describe online communities on the Web of Data.
• CIDOC CRM (Conceptual Reference Model) - An ontology for cultural heritage information, which describes the explicit and implicit concepts and relations relevant to the documentation of cultural heritage.
• Wine Ontology - An example used in [W3C OWL Guide](https://www.w3.org/TR/owl-guide/).
• Food Ontology - An example used in [W3C OWL Guide](https://www.w3.org/TR/owl-guide/).
• FoodOn - An ontology built to interoperate with the OBO Library and to represent entities which bear a "food role".
• Geographical Entity Ontology - An ontology of geographical entities implemented in OWL 2 and based on Basic Formal Ontology (BFO).
• rNews - An approved standard for using semantic markup to annotate news-specific metadata in HTML documents.
• Friend Of A Friend (FOAF) - A computer language defining a dictionary of people-related terms that can be used in structured data.
• vCard Ontology - An ontology for describing people and organizations. A mapping of the vCard specification (RFC6350) to RDF/OWL.

Vocabularies

• Dublin Core Metadata Element Set - A vocabulary of fifteen properties for use in resource description.
• DCMI Metadata Terms - An extension of the Dublin Core Metadata Element Set.
• IMI (Infrastructure for Multilayer Interoperability) Core Vocabulary - A Japanese controlled vocabulary consists of roughly 60 class concepts, 250 property concepts and words associated to them.
• Open Graph protocol
• RDF Schema (RDFS) 1.1 - A data-modelling RDF vocabulary used for defining RDF vocabularies.
• Schema.org Schemas
• SKOS (Simple Knowledge Organization System) - An RDF vocabulary for representing semi-formal knowledge organization systems (KOSs), such as thesauri, taxonomies, classification schemes and subject heading lists.
• DCMI Metadata Terms - An extension of the Dublin Core Metadata Element Set.

Mid-level Ontologies

• UMBEL (Upper Mapping and Binding Exchange Layer)
• MILO (Mid-Level Ontology)

Vocabularies

• Ontology Matching - Hosting OM (International Workshop on Ontology Matching) and OAEI (Ontology Alignment Evaluation Initiative).
• Alignment API - Ontology Alignment API specification. (implemented in Java)

Vocabularies

• Description Logics (DLs)
• F-Logic
• Description Logic Complexity Navigator

Vocabularies

• EYE - A reasoning engine which performs semibackward chaining and supports Euler paths. (Prolog)
• FaCT++ - The new generation of the well-known [FaCT](http://www.cs.man.ac.uk/~horrocks/FaCT) OWL-DL reasoner which uses optimised tableaux algorithms. (C++)
• Flora-2 (Ergo Lite) - A F-logic based reasoning system. (Prolog)
• Racer - A knowledge representation system that implements a highly optimized tableau calculus for the description logic SRIQ(D). (Common Lisp+Java)
• cwm - A forward chaining RDF reasoner. (Python)
• Hoolet - An implementation of an OWL-DL reasoner that uses a first order prover. It uses the Vampire prover for reasoning purposes. Other reasoners could also be used; communication with the reasoner is via the TPTP format which is understood by a number of theorem provers.
• KAON2 - A DL reasoner for the SHIQ(D) subset of OWL-DL, based on novel algorithms which reduce a SHIQ(D) knowledge base to a disjunctive datalog program. (proprietary, Java)
• How does a reasoner work? - An introductory article by Uli Sattler, Robert Stevens, and Phillip Lord
• HermiT - The first publicly-available OWL reasoner based on a novel “hypertableau” calculus which provides much more efficient reasoning than any previously-known algorithm. (Java)

Vocabularies

• SPARQL 1.1 - A set of specifications that provide languages and protocols to query and manipulate RDF graph content on the Web or in an RDF store.
• SPARQL-DL - A substantial subset of SPARQL that can be covered by the standard reasoning services OWL-DL reasoners provide. It is implemented in the Pellet reasoner.
• SPARQL-OWL algorithm - A sound and complete algorithm for answering SPARQL-OWL, SPARQL queries under the OWL 2 Direct Semantics entailment regime.
• [protege-user
• DL Query (class expression) - A query language supported by the DL Query tab plugin for Protégé based on the Manchester OWL syntax.

Vocabularies

• LinkML - A polymorphic semantic modeling language.
• SHACL (Shapes Constraint Language)
• ShEx (Shape Expressions)
• SWRL (Semantic Web Rule Language) - A rule markup language which extends the logical expressivity of the OWL language.
• SPIN (SPARQL Inferencing Notation) - shacl.html))

OWL-aware libraries

• Apache Jena Ontology API
• Owlready2 - A module for ontology-oriented programming in Python.
• OPPL - An abstract formalism that allows for manipulating ontologies written in OWL.

OWL-aware libraries

• Ontology Alignment Evaluation Initiative
• Association for Ontology Design & Patterns