Sql Server Mobile is a great new version of Sql Server CE which was released in VS 2005.
It provides a relational database engine with a tiny runtime, can replicate data to and from Sql Server 2005 and runs on many Windows mobile devices.
Well.. 'many', in that it wouldn't run if the OS wasn't Windows Mobile or Windows XP Tablet, which meant it wasn't an option for deployment to servers, desktops or even standard laptops...
Microsoft felt that these other OS versions should use Sql Server Express, which although is also great, is not particulary quick to install, and way too complicated and powerful for simple tasks.
So Microsoft has announced 'Sql Server Everywhere', which will be a one stop deliverable from your Smartphone to your enterprise Windows 2003 server
Origional blog entry here:
http://www.fastchicken.co.nz/blog/PermaLink,guid,0a7e0f66-79b6-4998-8e25-8f6b62104c24.aspx