Code.
.org
This is an online code browser that can be used to read the source code of many free software projects. It is created using the Woboq Code Browser generator.
It focuses on improving the code navigation with proper semantic highlighting and tooltips. Read more about it in our blog post. Inspired by KDevelop.
KDE
Many of the KDE repositories. http://kde.org.
Contains also 
Qt 4 and
Quassel (quassel-irc.org).
Qt 5
Sources of Qt5. http://qt-project.org. Including Qt Creator.
Contains 
Webkit
Linux
The sources of the linux kernel. (kernel.org)
glibc
The GNU C Library. (www.gnu.org/software/libc)
LLVM
The LLVM (Low Level Virtual Machine) compiler infrastructure. (llvm.org). Including Clang (the C/C++ compiler)
GCC
The GNU Compiler Collection. (gcc.gnu.org).
Boost
The Boost C++ libraries. (boost.org). 
All code on code.woboq.org was generated on linux x86_64.