Nexmo https://github.com/Nexmo/api-specification/blob/master/.spectral.yml.
Box https://github.com/box/box-openapi/blob/main/.spectral.yml
Digital Ocean https://github.com/digitalocean/openapi/blob/main/spectral/ruleset.yml
https://github.com/italia/api-oas-checker
Need an intro to Spectral ? See this post, with accompanying code here.