A useful resource for finding ontologies is the Ontology Lookup Service (OLS) (https://www.ebi.ac.uk/ols/index). It includes many of the ontologies that are likely to be of interest to behavioural scientists but also many ontologies that are not very well constructed.

Ontobee (https://ontobee.org/) contains ontologies used in biomedical science that conform to a set of standards set by the OBO Foundry (https://obofoundry.org/)

Probably the most widely used ontology in science is the Gene Ontology which has gone a long way to unifying molecular biology.

We have created a resource for people working in behavioural and social sciences that aims to curate ontologies in this domain. It is called the Behavioural and Social Sciences Ontology (BSSO) Foundry (http://www.bssofoundry.org/)