Oracle Client Express Edition

Oracle Database 11g Express Edition (Oracle Database XE) is an entry-level, small-footprint database based on the Oracle Database 11g Release 2 code base.

It's free to develop, deploy, and distribute; also it is fast to download and simple to administer.
Oracle Database XE is a great starter database for:
- Developers working on PHP, Java, .NET, XML, and Open Source applications
- DBAs who need a free, starter database for training and deployment
- Independent Software Vendors (ISVs) and hardware vendors who want a starter database to distribute free of charge
- Educational institutions and students who need a free database for their curriculum