"LocalDB is created specifically for developers. It is very easy to install and requires no management, yet it offers the same T-SQL language, programming surface and client-side providers as the regular SQL Server Express. In effect the developers that target SQL Server no longer have to install and manage a full instance of SQL Server Express on their laptops and other development machines.
Localdb is a minified version of SQL Express that require less number of pre-req to install and offers a fast, zero-configuration installation. – Chirag Shah
In SQL Server "Denali" we decided to change the approach and introduce a dedicated version of SQL Express for developers - LocalDB that delivers the simplicity and yet is compatible with other editions of SQL Server at the API level.
LocalDBManager.exe was the original name of the tool. Just before shipping CTP3 we decided to change the name to SqlLocalDB.exe, since LocalDBManager.exe seemed a little bit over the top for a simple command line tool. "Manager" part of the name suggests something much more comprehensive than SqlLocalDB.exe, something like the old SQL Server Enterprise Manager or IIS Manager. - Krzysztof Kozielczyk
Also, by making LocalDB a better SQL Express for developers, we hope to be able to improve the regular SQL Express to be a better free SQL Server. We'd be very happy to hear your feedback in this area, especially if you're using SQL Express as a database server and find any issues caused by the new features that were introduced to fit the needs of developers and desktop environment.
"Now that SQL Server Compact 4 has been released, some developers are curious about the differences between SQL Server Compact 4.0 and SQL Server Express 2008 R2.
I have updated the comparison table from the excellent discussion of the differences between Compact 3.5 and Express 2005 here to reflect the changes in the newer versions of each product.
Information about LocalDB comes from here and “Denali” CTP3 Books Online. LocalDB is the full SQL Server Express engine, but invoked directly from the client provider. It does not support Fulltext Search, and I doubt it support Merge Replication. It is a replacement of the current “User Instance” feature in SQL Server Express
While the chart is a few months old now, I still thought it outstanding seeing this kind of comparison, as I have the same questions, i.e. "What's the diff?" Now I'm in a better place... lol :)
Related Past Post XRef:
SQL Server Compact 4 vs SQL Server Express 2008 R2 Side-by-side feature comparison