I am currently working on software that must emit SNMP traps for SNMP versions 1 & 2 and possibly v3 in the future. I have downloaded several and found them to be either too complex or too simplistic. All I want is to view traps and analyze the data structures within them, and the ability to import my custom MIB's. The best I have found so far is ireasonings MIB Browser, but would be greatful for any nice alternatives.
netsnmp - should do everything you're after, with a variety of language bindings to suit every taste.
We were using netsnmp until I discovered the iReasoning tool. After using the personal edition for a couple of years, if I ever have a requirement to work with SNMP v3 then I won't mind shelling out the $295 for the nice pointy clicky UI.
The only monitoring tools I've used that utilize SNMP monitoring are Nagios, Zenoss, OpenNMS, and the proprietary product from my company - but they're for full network monitoring.
How many devices are you looking to monitor? If it's only a couple, @Andrew's suggestion of netsnmp may be sufficient.
Out of the three (Nagios, Zenoss, OpenNMS), which was most effective for monitoring SNMP devices? I need a tool that will allow me to monitor 300+ devices. I'd like to be able to load the MIB and configure events for each trap type.