NetFunctional is about to release an SNMP based app, so I’ve been testing it against all sorts of various devices. Since OSX is Unix/BSD based, it can be an SNMP agent too, once you configure and enable it. Here’s how:

Configure SNMP
1. sudo vi /etc/snmp/snmpd.conf
2. Find the line
   rocommunity public default .1.3.6.1.2.1.1.4

3. Replace it with (note: you may wish to change ‘public’ to something less default):
   rocommunity public default

4. Save and exit

Then simply enable SNMP to be loaded all the time (this works on Snow Leopard and Lion)

sudo launchctl load -w /System/Library/LaunchDaemons/org.net-snmp.snmpd.plist