PGT is a free software for Windows that enables mass-scripting with Python. It is optimized for mass-configuration of routers and switches, and is extensible with .NET-based network configuration tools. Its visual scripting interface is designed like a flowchart.

One of the standout features of PGT is its ability to connect to remote devices even when a direct, routed connection is not available. Instead, jump servers and routers can form a path, hop-by-hop, towards the destination. This makes it an incredibly valuable tool for network administrators dealing with complex systems.
Another aspect I appreciated was how easy it was to generate a device script, or create one in Excel and import it for execution. Additionally, PGT's modular architecture supports external class libraries for .NET languages to perform custom actions via a scriptable terminal interface. This makes it an excellent development platform, and it can even be used as an SSH/Telnet library for applications.
But PGT isn't just about connecting to devices directly - it also supports a chain of jump servers for even greater flexibility. And for those who are more familiar with VBS/WSH/PowerShell scripting, PGT exposes its functionality through COM objects.
All of this versatility, power, and efficiency has been proven in real-life production environments, including data centers, and has been tested on over 50,000 devices. If you're in need of a robust, scriptable, and extensible network configuration utility, I highly recommend giving Pretty Good Terminal a try.
Version 7.0.0.1:
Python scripting support was introduced which combined with the Visual Script editor makes very easy to develop complex scripts. The built-in Python script debugger and automatic code-completion in Python Interactive window gives a real IDE experience.
Extensive documentation included.