The Common Open Research Emulator (CORE) is a tool for emulating networks on one or more machines. You can connect these emulated networks to live networks. CORE consists of a GUI for drawing topologies of lightweight virtual machines, and Python modules for scripting network emulation.
The NCTUns is a network simulator and emulator. Each version adheres to only a selected GNU/Linux distribution of fedora (The latest NCTUns 6.0 adhering to fedora 12). We try to port the latest NCTUns 6.0 to Ubuntu 10.04 or later versions.