This is a huge day for developers: Oracle Database 10g Express Edition (Oracle Database XE, for short), a no-frills edition of the Oracle 10g database, is here, and it's free. Yeah, I said "free" -- to download, develop, deploy, and distribute. (Database size, CPU, and memory restrictions apply.)
Just as important, XE is easy to download (about 150MB) and install.
So if you're a .NET, Java, or PHP developer who wants to plug into Oracle's respective development stacks without worrying about a future messy migration, a learning or first-time DBA, or even a student, you're going to be pleased. Plus, ISVs will be able to happily accomodate this small-footprint edition onto a CD along with their own software.
Download the software for Windows or Linux x86 and get more info at oracle.com/technology/xe.
