A full-sized ADO.NET data provider featuring the Connection, Command, DataReader, DataAdapter and CommandBuilder components. Apart from the connection string, you should be able to use the same database code for OleDb and TurboDB data access.
The intelligent data access layer, connects .NET components to relational databases with little or no code changes and no code generation. By Revelation Technologies.
A proxy-caching database server optimized for the .NET environment. It supports Oracle, SQL Server, DB2, PostGreSQL, FireBird, and MySql. By JHOB Technologies.
A software component which allows to programmatically create SQL queries in runtime using a convenient .Net Object Model, thus creating an abstraction layer over SQL. [Open source, GPL]