To be impartial, I've also checked out, used, or heard of these other free database applications that some might find more appealing than MySQL. Heck, I'll use any database that is relational, is SQL-compliant, has a driver for my programming language, is known-good in the industry for the kind of application I am developing, and is (almost) free - unless the project requires using a specific product.
The free database applications:
- PostgreSQL: Extremely scalable, open-source, object-relational.
- Firebird: ANSI SQL-99 features, Open-source, freeware, based on Interbase.
- Apache Derby: Open-source, implemented in Java.
- H2 Database Engine: Open-source, Java SQL database engine with embedded, server and cluster modes.
- Hypersonic SQL: Open-source, created in Java, small. No longer being developed, but existing versions work well.
- SQLLite: Self-contained, embeddable, zero-configuration SQL database engine. Great for desktop applications.
- Microsoft SQLServer Express: Lightweight version of Microsoft's commercial SQL Server database.
- Oracle Database 10g Express: Freeware edition of Oracle's high-grade 10g database.
Finally, perhaps it's nothing to worry about, but the future of MySQL long term is uncertain. The company was bought by Oracle, and I suspect they will want to monetize the acquisition. They make expensive and enterprise-grade databases already, and I do not see a huge incentive to keep a (good enough, production-grade) free database around. Time will tell.