1. SNMP Polling
2. SNMP Traps
To download it, just go to http://www.manageengine.com/products/mibbrowser-free-tool/index.html
This company seems to have some other interesting free networking tools, see the link below for the full list:
By the way, talking about other free tools, I have been using other two that have helped me in some matters, one of them is for keys/certificates management and the other is for LDAP browsing:
Portecle - Extracts and converts keys and certificates - http://portecle.sourceforge.net/
ADExplorer - Connects to a LDAP server so you can verify every single LDAP object - http://technet.microsoft.com/en-us/sysinternals/bb963907.aspx
Do you guys use any other tools to help somehow performing your day to day work?