From what I can tell everybody uses net-snmp, and from what I've seen the documentation is atrocious.

To send and catch a trap

Here is the bare minimum to send and catch a trap.

# /etc/snmp/snmptrapd.conf
authCommunity log,execute,net public

In one shell:

snmptrapd -nf -Lo

In another shell:

snmptrap -v 2c -c public localhost "" \
NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification netSnmpExampleHeartbeatRate i 123456

To snmp walk your machine

The default /etc/snmp/snmpd.conf appears to be adequate.

Run: snmpd -fd

In another shell: snmpwalk -c public -v2c localhost

The api

The example code to do a GET is pretty good, but to catch a trap? Not so much.

And as I write this the help page is broken snmp_api