There are many open source database management systems (DBMS) available for use. Some popular open source DBMS options include:
MySQL: a popular open source DBMS that is widely used for web-based applications and is known for its speed, reliability, and ease of use.
PostgreSQL: a powerful open source object-relational DBMS that is known for its strong support for SQL standards and its ability to handle a wide range of workloads.
MariaDB: a fork of MySQL that is widely used as a drop-in replacement for MySQL and is known for its high performance and scalability.
MongoDB: a popular NoSQL DBMS that is designed for storing and managing large datasets and is known for its flexibility and scalability.
Redis: an in-memory data store that is widely used as a database, cache, and message broker and is known for its high performance and flexibility.
Cassandra: a distributed NoSQL database that is designed for handling large amounts of data across multiple servers and is known for its scalability and fault tolerance.
There are many other open source database options available, and the best choice for a particular project will depend on the specific needs and requirements of the project.