Oracle releases free database
Oracle has released its entry-level database, Oracle Database XE, which can be used for development or deployed as a live system at no cost and runs on 32-bit Linux.
Called a "starter" database by Oracle, all applications and data created in XE can be ported to Standard Edition One, Standard Edition, or Enterprise Edition without change.
The license limits the scalability of the database. The database may not exceed 4GB; only a single instance of XE may be run on any one server; it may only use one processor in a server; and it can only use up to 1GB of RAM. The database is also limited to 32-bit operating systems.
If you're happy with those limitations, the database is free to download, develop for and distribute.