Empty db for sqlexpress to use with umbraco.
Simply put in app_data folder and use this connection string:
Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\UmbracoDB.mdf;Integrated Security=True;User Instance=True;Database=UmbracoDB
I try to use new SQLCE, which don't need installation, but I found out, that there are a lot of packages (and same starterkits) which don't work with SQLCE. So I go back to this embeded db when developing or testing and put it here for other peoples without Visual Studio.
Another benefit for me is that my hosting company can automatically migrate it to full sql when I need to deploy completed solution. Plus you can easy backup/restore (see note in wiki article)