Cisco CDP Monitor
Cisco CDP Monitor is an efficient network diagnostic and troubleshooting tool. It is very useful for network administrator and network engineer. At first, Cisco CDP Monitor is a CDP agent for windows host. It is able to use the CDP(Cisco Discovery Protocol) which is a private protocol and is... So the LAN Management Solution and the Routed WAN Management Solution of CiscoWorks 2000 Campus Manager can get these information and show the total topology of your network in graphics mode, not only the Cisco network devices, but also your PC and host.
http://www.tallsoft.com/cdpmonitor_setup.exe - 917Kb - Download - Screenshot

AdventNet Simulation Toolkit
AdventNet Simulation Tool comprises easy-to-use, GUI-based agent simulator and network simulator for testing, training and demonstration of network management applications. The network simulator enables network simulation of 50000+ SNMP (v1, v2c, v3), TL1, TFTP, FTP, Telnet and Cisco IOS... Ability to simulate 50000+ agents simultaneously for scalability testing, trap simulation for fault management testing, configuration of device values and simulation types for performance testing, behavior simulation for testing realistic/negative test scenarios across network devices, start/stop of...
http://www.adventnet.com/products/simulator/download.html - 16Mb - Download - Screenshot

PortMarshaller
PortMarshaller is a software-based TCP/IP port forwarder and network monitoring service. The software accepts connections on a particular TCP port, and establishes connections to a different TCP port to fulfill requests. This capability offers a solution to various network topology problems. ... Optionally integrates with Internet Information Services (IIS) for its advanced abilities. ... Administrative web interface allows the monitoring of connection and data transfer statistics.
http://www.portmarshaller.com/portmarshaller.zip - 303Kb - Download - Screenshot

NetDecision
NetDecision is the affordable alternative to expensive and complicated high-end network management systems. Also, it's easily configured to match your precise network environment, scalable to accommodate growth, and simple to administer. Features: * Multi-level network topology. ... * CIM-compliant network model. ... * Reports to help you analyze your network uptime, capacity utilization, and response time. ... Network Manager continuously polls the mapped devices (and services on the devices). ... * Network Discovery.
http://www.netmechanica.com/downloads/ - 16Mb - Download - Screenshot