1. Amazon Relational Database Service (RDS)

They offer a a free usage during the first year.

• Amazon Aurora
• RDS for MySQL
• RDS for PostgreSQL
• RDS for MariaDB
• RDS for Oracle
• RDS for SQL Server
• Amazon RDS Custom

2. MongoDB Atlas

They have free 512MB / project.

• MongoDB database hosting

3. Filess

They have a free plan forever with free backups.

• MySQL
• MariaDB
• MongoDB
• Postgres

4. bit.io

Managed PostgreSQL database service. 1 database, 10GB storage, 1 CPU and 1GB Memory (burst).

• Postgres