We leverage MongoDB in a large number of client projects and always recommend MongoDB atlas for hosting. While you can roll your own and manage all of the infrastructure required to host a MongoDB database, for the time/cost it's just not worth it. Atlas is well priced for what it offers and it is easy to get a database up and running in just a few minutes. That plus all of the security and backup features make it an easy choice for us.
SAP HANA - SAP HANA is an in-memory, column-oriented, relational database management system.
MySQL - The world's most popular open source database
Ninox - Ninox is a human-friendly database. Create your own Business Application with Ninox that matches your workflow. Ninox lets you integrate CRM, ERP, HR and many more...
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
Amazon Aurora - MySQL and PostgreSQL-compatible relational database built for the cloud. Performance and availability of commercial-grade databases at 1/10th the cost.
Oracle Database 12c - Simplify database management and automate the information lifecycle with maximum security.