> I'm trying to find a small footprint open source database which I can
> access from Java clients on a number of different platforms, including
> Mac OS 9. Mac OS 9 only has (and will only ever have) JDK 1.1.8, so
> the JDBC driver will need to be able to run in Java 1.1.8. I haven't
> been able to determine whether Firebird's will.

Unfortunately, JayBird requires JDK 1.3.x and higher.

> If not, are there any alternatives?

You can check InterClient 1.6 or 2.01, should work. You can get
sources from Firebird project at SF.net (module name "interclient/16"
or "interclient/20"). However you have to build it yourself (and if
you want to run server on Mac OS, you will have to build native
component of it yourself). Also be prepared to fix bugs in the driver
yourself - there's nobody from Firebird project supporting it.

I would consider in your case using 3-tier model, you will have more
freedom in developing main functional part in the middle tier while
keeping an option of having client that runs in JDK 1.1.x. In this
case RMI might be an interesting option.

Also you can check JDataStore from Borland, it runs in JDK 1.1.x, but
it is not open source and not free.

Best regards,
Roman Rokytskyy