Steve,

I think that the only way to have a DBMS that works on all the three platforms, you probably need a Java solution. If you visit Freshmeat.net or, better, SourceForge.net you can do a search and find a good number of possible solutions, like HypersonicSQL (now called HSQL DB) and some others. Searching on the net you can find other java solution like InstantDB or Jeevan 3.0.


If you think of using MacOS X, then you reduce the number of platforms to 2 (WIndows and *nix), and so you can use MySql and maybe PostgreSQL although I don't remember having a free Windows version of it.