I just uploaded an initial version of Visual Dooby, a portable lightweight database client.
This initial release is quite limited. You can currently only connect to a SQL Server database, the database browser only displays tables, views and columns, and you can save the results of a query to an XML-file.
Some nice features are the advanced customizations when saving to XML, the visualization of data types in the result grid and the grid row numbering.
You can download it from Box.