Support for Informix via the dbaccess user interface program, which means that it is theoretically possible to compare the performance of Informix, MySQL, and PostgreSQL on the same system under the same conditions.
Version 0.4 of OSDB includes support for MySQL 3.23.30.gamma (callable interface, mysql client program), PostgreSQL 7.0.3 (callable interface, psql client program, and Embedded SQL. The mysql client program support is definitely broken, and there may be a bug or two remaining in the rest of the code, too.