Oracle Express Editon

These are just some general points that might save you a bit of time and head scratching if you decide to give Oracle XE a go:

First, let's start with the good:

It's free to download and develop on
It's free to deploy (including distribution, as long as you make the other party aware of the licensing details)
It is the first really simple installation on either Windows or Linux that I have ever seen Oracle do
The included tools are superb and very modern and AJAXy

However, there are limitations:

--> Although you can install it on a multiple CPU machine, and it will run on one, it will only use one CPU on that machine.

--> It will only use a maximum 1 gigabyte of memory (again, it will run on machines with more memory; it just won't use it)

--> It has a database size limit of 4 gigabytes for user data (this is all available to the user; system data is counted outside of that 4 gig limit)

--> Only one instance of Oracle XE can run on any given computer.

You can download Oracle XE software from following link:
Download Link