What options might be applicable for a non-open source (commercial) program that is to be distributed to many people with an embedded database?
MySQL proves too expensive, and I'm sure other commercial ones are as well.
The databases would only have one or a few concurrent users (as they'd be individual to the user), but would need to be able to manage a very large number of different databases, tables, fields, and records while not caving under performance requirements...any suggestions?
Please list as many free or close to free options as you can think of (java-compatible, of course).
There's a lot of them around. Apache took delivery of a previously commercial offering from IBM a few months ago, released now under the name Derby.
Then there's HSQLdb, rather nice but maybe too lightweight for your purpose.
Borland sells JDataStore, which may well be too expensive.
Sun I think has something as well.