Open Source Database Management Systems

Subsets of SQL

mSQL by Hughes Technologies

mySQL by T.c.X DataKonsult AB

SQL

PostgreSQL

sapdb.org

Discussions and Comparisons

nice discussion about the pros and cons of MySQL (versus PostgreSQL and Oracle)

Tim Perdue's comparison of MySQL and PostgreSQL

Libraries (Embedded Databases)

Sleepycat's Berkeley DB

GiST

Indexes

! Christopher Browne's RDBMS Index

Pal's Linux RDBMS Index by Pal Domokos

Database index by ACM SIGMOD

dmoz.org index