Cortex CMS is inspired by many CMSs already in the wild, including but not limited to:
WordPress - By far the most popular CMS due to its inherent simplicity and great content creator experience. Lacks flexibility and advanced distribution.
Drupal - Supports slightly more advanced distribution models, but lacks a great content creator experience, is not headless (lacks an API, so it does not support more advanced distribution), and can be very difficult to maintain and scale.
HippoCMS - Supports advanced distribution models, features a novel backend (JCR), is headless, but is Java-based and potentially unwieldy.
Contentful - Supports advanced distribution models and is headless, but lacks a great content creator experience and is closed-source.
Prismic - similar to Contentful, but isn't quite as feature-rich, and is also closed source.
GraphCMS - The closest analogue to Cortex CMS. Fully headless with a custom content model, the backend to this CMS is still closed-source.