Nullsoft Database Engine
From Winamp Developer Wiki
The Nullsoft Database Engine powers the local media library, history, and the CD metadata database. It is relative simple and has a small query language. Most winamp data can be found in the file 'main.dat', which on Windows machines is usually stored in a location like "C:\Documents and Settings\<username>\Application Data\Winamp\Plugins\ml\" (citation needed).
For more information describing the Nullsoft Database Engine format, see here.
- NDEPHP - an open source project that can read the database using PHP.