Suggested "Free" Tools you shouldn't be without

Putty
http://www.chiark.greenend.org.uk/~sgtatham/putty/
PuTTY is a free implementation of Telnet and SSH for Windows and Unix platforms, along with an xterm terminal emulator.
 
Notepad++
http://notepad-plus-plus.org/
Notepad++ is a free source code editor
  
NET-SNMP
http://www.net-snmp.org/
Net-SNMP is a suite of applications used to implement SNMP v1, SNMP v2c and SNMP v3 using both IPv4 and IPv6. The suite includes:
 
Wireshark
http://www.wireshark.org/
Wireshark is the world's foremost network protocol analyzer. It lets you see what's happening on your network at a microscopic level. It is the de facto (and often de jure) standard across many industries and educational institutions.
 
Free SNMP Walk Tool for Windows and Linux
http://www.manageengine.com/products/mibbrowser-free-tool/
SNMP MIB Browser is a complete tool for monitoring SNMP enabled devices and servers. You can load, view multiple MIB modules and perform GET, GETNEXT and SET SNMP operations. This tool is easy to use and allows you to view, configure and parse SNMP traps.