I've noticed on Slashdot.org (
http://slashdot.org/articles/00/06/28/1454220.shtml ) that MySQL has
been released under the GPL, which means that it is open source and free
for non-commerical and commercial use.
There is also (the neverending) discussion of PostgreSQL vs. MySQL.
But: without transactions it's not a real database ;-)
Poul L. Christiansen