This is a great alternative to Access.  I've used this database for web sites and desktop apps.  There are drivers for virtually any major language (.net, java) and also ODBC drivers.  There are some nice visual front ends for this database but the command line utility is elegantly simple to use. 

Don’t expect features like stored procedures here as this is a very compact and light weight database.  Also the data typing is rather loose so don’t rely on the database to verify data types (which you shouldn’t do anyway).  It appears that PHP is including this in the distribution so this database will become widely available. 

This is a great database to use for prototyping and distributed or mobile applications.  Of course it lacks enterprise features but that may be a bonus in some situations.  The speed of the database is unbeatable so this is definitely a tool to look at if you need a fast light weight portable database.