The headless CMS market is exploding, and there are some interesting open source alternatives like Directus and soon GraphCMS. Contentful is in the lead for proprietary options, but there is room for open source. Another new option is GraphQL enabled Gentics Mesh.
Graph Databases are becoming more common place in social media, dta processing, content management and other applications developed by millions of people around the world. There are query languages like Cypher for Neo4j, etc. But who does Graphs better than Facebook? Arguably no-body. This is why GraphQL, now Open Sourced by Facebook could be the SQL of Knowledge.