Project Nami is a fork of WordPress which is deigned to work with Microsoft’s SQL server in place of MySQL. The idea was to make it easier to use Azure which does not have a native MySQL server like 99% of other web hosts.
Generally Nami is identical to WordPress with only the database connection module changed. This means the code base is slightly behind the curve as the developers have to constantly revise each version of WordPress.
phpBB is one platform we are aware that does support SQL Server natively but CMS systems are all MySQL only. It appears as though they were developed on a LAMP server for a very long time before Azure was created.
Generally SQL Server is used more with Windows Server and .NET type web sites. Microsoft will have to provide more code samples in PHP and C# for connecting to all databases so that conversion utilities and backups are easier.
The main problem is that Project Nami has many compatibility problems. Themes and Plugins may not work.