I recently needed to change my modem due to a technology change, and the new modem did not like to talk SNMP to the big bad Internet. However, it does very happily do so to the local network. While this is probably not an issue for many, I do not have any decently powered server at home, only a rented one outside to do my network statistics.
To overcome the issue, I needed to get my OpenWRT -router to bounce the SNMP packages to the modem, and relay replies back. And while it is seemingly possible with net-snmp snmpd, the configuration is far from straightforward and the OpenWRT packages seem to be lacking in that regard.
Hence I wrote my very own, very simple, proxy daemon. It is not smart at all and simply sends SNMP replies back to the last one to make a request. But it works for my purposes. If you are in similar need, you can grab the source.
I also made a slightly more complex version that allows redirection of different community names to different SNMP servers/agents (no community name rewriting).