DotNetNuke can currently be run on at least two database platforms - Microsoft SQL Server and Oracle. In the 2x days of DotNetNuke, it was also possible to run DotNetNuke using Microsoft Access which was more easier/familiar to the some of the community than SQL Server or Oracle.
The Firebird® Data Provider is a new sub project under the core which will allow DotNetNuke to run using a Firebird Database. Firebird® is a relational database which runs on Linux, Windows and other flavors of the Unix Platform. It is ANSI SQL compliant and has a very small footprint in comparision to MS SQL Server or Oracle. It can also be run in an embedded mode requiring little or no interaction from the end user.
The goal of the Firebird Data Provider is to offer yet another alternative for DotNetNuke users who do not wish to use SQL Server or Oracle.
For those interested, you can get some more information on Firebird® from here.
This project was started by various volunteers with the desire of offering another viable alternative for DotNetNuke and thereby increase the overall usage of DotNetNuke. A large portion of the provider was contributed by Sanjay Mehrotra who also is the author of the Oracle Data Provider.