Polyglot Persistence for .NET with PostgresSQL and Marten with Jeremy Miller on the Hanselminutes Technology Podcast: Fresh Air for Developers
"Polyglot Persistence for .Net Systems using the Rock Solid Postgresql Database"
Marten - Marten as Document Db
Document Queries - MassiveJS | A Postgres-centric Data Access Tool
"PostgreSQL is a powerful, open source object-relational database system. It has more than 15 years of active development and a proven architecture that has earned it a strong reputation for reliability, data integrity, and correctness."
Both AWS and Azure support PostgreSQL as a cloud database service.