NetworkX

It comes with a graphing utility, to help user better understand network usage and functions.

Features:

• Allows for 1M nodes, 10M edges
• Includes standard graph-theoretic and statistical physics functions
• Easy exchange of network algorithms between applications, disciplines, and platforms
• Includes many classic graphs and synthetic networks
• Nodes and edges can be "anything" (e.g. time-series, text, images, XML records)
• Exploits existing code from high-quality legacy software in C, C , Fortran, etc.
• Unit-tested
• Additional benefits due to Python:
• Allows fast prototyping of new algorithms
• Easy to teach
• Multi-platform
• Allows easy access to almost any database