Blender has two build toolchains – scons and cmake. But Google switched away from scons in pepper and are using makefiles (which is sad because they had a pretty disciplined way of using scons).
V8 for Chromium uses gyp instead of scons now.
Libjingle (also Google) uses both gyp and scons.
Native Client might be supporting both? But comment above about pepper contradicts. https://code.google.com/p/nativeclient/issues/detail?id=2731
Several people have extended Scons in one way or another.
- Intel’s Parts – http://parts.tigris.org/
Ninja is yet another build system, and someone has integrated it with Scons. Or, rather, generate a Ninja script from an Scons dry run.