I just released DB_Table 0.22.0 beta. This is the first new release since July 7, and the first beta release. It has been pretty well tested against MySQL and PostgreSQL, but should work with Oracle, MS-SQL, and SQLite as well. I'd be very happy if MS-SQL or Oracle users could provide feedback on how well DB_Table works on those systems; please email me if you would like to provide a report.
The ideas behind DB_Table are simple: embed your column definitions and baseline queries within the PHP class. Then you can call select('myQuery') and get your results, or call insert($myColumns) to insert a new row, and so on. Becuase the class knows the column definitions, it can validate the new data before even connecting to the database; you can extend the validation method to cover all kinds of data. This also lets you automatically create a form based on the column definitions with HTML_QuickForm. DB_Table automates table creation; if a table does not exist in the database when you call a DB_Table object, DB_Table can create it right then, along with indexes -- all because the column definitions are embedded in the class.
DB_Table also provides a poor-man's version of data type abstraction. This element is somewhat controversial. We all know that different database systems keep date and time data in different formats, and it becomes an ... interesting ... task to create portable SQL statements that will work properly against those different systems. Metabase and its cousin MDB do this by providing translation functions to convert the native RDBMS format to a common format on retrieval and insert/update, but they are not exactly fully automated.
The DB_Table abstraction method (such as it is) instead forces the database to store the date and time as fixed-length strings in ISO-standard format. While this is going to give most database administrators a case of the screaming rants, it is a very workable solution for low- and mid-range applications where portability, not 100% optimization and efficiency among multiple systems, is the paramount concern. This is particularly good for those of us who write applications intended for distribution and need to know for sure that the app will work on a wide range of databases (with minimal effort). For example, YaWiki uses DB_Table to great effect.
You can read the full DB_Table documentation here.