This is a cross reference designed to display source code. Sources may be retrieved via cvs, svn, git, apt, or through some other process.
It's possible to search through an entire source text; or to search for files whose name matches a pattern; or to search for the definitions of particular functions, variables, etc.
The individual files of the source code are formatted on the fly and presented with clickable identifiers. An identifier is a macro, typedef, struct, enum, union, function, function prototype or variable. Clicking on them shows you a summary of how and where they are used.
The free-text search feature is implemented using Glimpse, so all the capabilities of Glimpse are available. Regular expression searches are especially useful.
(Don't use a web-crawler to try and download all of these pages; the CGIs will feed you several gigabytes worth of generated HTML!)
(That's beyond the nearly ∞ gigabytes worth of content that is indexed here.)