Microsoft has worked hard to make .NET and SQL Server a powerful combination - and VistaDB brings that capability to a small, easy to deploy package. Instead of having to ship a large installation which has to be set up independently for your application to work you can just ship 2 MB of extra assemblies with your .NET application. It's easy to make applications that start with VistaDB and scale up with SQL Server, all from a common codebase.

Compared to Microsoft SQL Server...

Tiny Distribution: The core engine is just over 1MB in size when deployed (often 450kb when compressed) compared to over 132MB for the compressed SQL Express installation.
Cross-Platform: Works on 32 or 64 bit and can be deployed under Mono and .NET
Full Database Encryption: Instead of just encrypting individual fields or tables the entire database file is encrypted.
No Privileges Required: VistaDB can be used even by guest accounts, not requiring any special OS permissions to create or work with databases or be deployed.
Easy Database Distribution: Since a database is just a file including schema and data it's easy to make backups and create new databases just using standard file operations.

Compared to Other Embedded Databases...

100% Managed Code for Simple Deployment: Only one set of assemblies is needed, covering 32 or 64 bit, Intel and ARM processors.
Impressive Commonality with Microsoft SQL Server: Data types, User-defined Functions, and even Stored Procedures can all be shared between SQL Server and VistaDB
FIPS-compliant Full Database Encryption: Securely encrypt the entire database including schema and data using FIPS-compliant AES encryption
Visual Studio Integration: Full designer support within Visual Studio including the Dataset designer, Entity Framework Designer, schema management, and query building.

.Net Database Basics
If a relational database doesn't have advanced features like updatable SQL Views, true referential integrity, cascading updates / deletes, table value params, T-SQL stored procedures, CLR Triggers, and CLR stored procs then why would you bother? Database engines that only provide basic ADO.NET features are a waste of your time. VistaDB is the most advanced embedded SQL desktop database engine in the world. We built VistaDB from the ground up to be a managed database engine, this is not some unmananged C++ database with a .Net wrapper!

Support VistaDB and SQL Server from the same executable?
Do you wish you could build a single executable that supported both SQL Server for multi user and another database on the desktop? We know how hard it is to build applications that support both desktop and client server from a single executable. VistaDB syntax contains the most commonly used features from SQL Server. All of our syntax will scale up to SQL Server. This means you can use one codebase in your product and run it against SQL Server and VistaDB. VistaDB fully supports the ADO.NET Provider Factory model. This allows you to dynamically load the database engine at runtime based upon application preferences. Many companies use VistaDB on the desktop and SQL Server for larger deployments. It is not the easiest way to write database code, and there is much less documenation around to explain how to do some things in Visual Studio. But if you take the time using Provider Factories can be a powerful runtime feature for your application.

.Net Database Admin Tools?
Some embedded databases give you an engine and nothing to edit or maintain the actual database. You usually have to purchase a third party DBA tool, build you own, or tell users to go download the large bulky tool from the vendor.