Actually, our plans for 7.0 are way up in the air at the moment. There are so many possibilities that we need to explore before we decide what should be done...
We currently have no plans to create an official port of UBB to any RDBMS.
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Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.