What's different between SQL Server Express and Compact?

Sometimes, developers as me what is different between SQL Server Compact 3.5 and SQL Server Express Edition. Shortly put, the idea with Compact is to be an embedded, application-managed database, while Express is meant to be a regular, but simple solution for generic SQL needs.

Although the material covers SQL Server version 2005 only, Microsoft has written a nice paper in Word format about these differences, and also gives ideas on how to select the correct database for your needs. Recommended reading, if you are interested in SQL Server Compact edition. Coming up is a quick tip about this embedded database.