[From eWeek]
A major change since SQL Server 2000 is the introduction of the free Express version of SQL Server 2005, designed for smaller-size database applications and to spur developer interest.
Oracle recently introduced a beta of its own free offering, the forthcoming Oracle Database 10g Express Edition.
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http://www.eweek.com/article2/0,1759,1894886,00.asp?kc=EWRSS03119TX1K0000594