SleepyGraph is a callgraph visualization tool for the VerySleepy profiler. Primary target platform is Windows, since VerySleepy is profiler for Windows. However, SleepyGraph itself is multiplatform (written in Python, but don't worry, installer contains all necessary dependencies).
Click on the screenshots to see full size images.
Screenshot: Callgraph of simple recursive program
Screenshot: Partial callgraph of a large application
Unless you are planning on developing SleepyGraph, downloading the Windows installer is the easiest way. (Though on Linux you may want the sources).
You'll find all files (Win32 installer, source archives) in the files section.
Get the code by cloning the repository:
hg clone http://sleepygraph.hg.sourceforge.net:8000/hgroot/sleepygraph/sleepygraph
or browse the repository online.
The Windows installer includes all of these, you'll need them just for development or running under a *nix system. Most major linux distros have them in distro repositories, just install them (look at INSTALL.txt in the source package).