OpenAPI Special Interest Groups, or "SIGs", are the OpenAPI Initiative's way of focusing work in particular areas. SIGs may start with just a Slack channel to gauge interest. SIGs with enough traction to produce work may have their own GitHub repositories and regular Zoom calls, and ultimately produce work that becomes part of, or a companion to, the OpenAPI Specification.
See the OAS community repository for a complete list of SIGs, and for more information about forming a SIG.