ng_fwdswitch is a FreeBSD kernel module based on the netgraph infrastructure that works as a basic packet forwarding engine. It will classify inbound IP packets using their source or destination address and forward them to the appropriate outbound interface. It could be used as an IDS helper, say to split "coherent" traffic across several sensors.
oom_ext is a Linux kernel module that reserves memory that is freed right before the OOM-killer is invoked to allow for large processes to exit nicely. This could be useful in a clustering environment to allow for a monitoring daemon to notify a sysadmin before an out of memory condition.