SQLite is a ACID-compilant Relational Database Management System. The whole package comes up to only 500Kb approximately. SQLite was created by D. Richard Hipp and the source code of which is in public domain.
The main feature of SQLite is its not a separate process instead SQLite Library is Linked in and hence integrates with the part of the application. It follows 3 out of 4 rules of database transactions that are Atomic, Isolated and Durable. As it has no foreign key attribute hence it doesn't satisfy the consistency requirement. SQLite also supports and triggers the complex queries. Its also a dynamically typed i.e. types are assigned to individual values instead of individual columns. Also several threads and processes can simultaneously access the database.
SQLite can be used with a large number of programming languages including BASIC, C, C++, Common Lisp, Java, C#, Delphi, Lua, Tcl, R, PHP, Perl, Ruby, Objective-C (on Mac OS X), Python, newLisp, Smalltalk, using connection engines.
Source: http://www.sqlite.org/,http://en.wikipedia.org/wiki/SQLite