[armon]

The two offer very different trade offs and have different architectures. Serf is an AP system, meaning it trades of consistency for availability. 90% of your nodes can be down and a Serf cluster will continue to operate. It does offer a primitive set of features, but it is useful for a wide variety of tasks such as configuring a memcache pool, load balancers, P2P VPN topologies, etc.

Consul is a CP system, meaning it trades availability for consistency. It has a much more limited ability to tolerate failures. However, its more central architecture allows it to support a richer feature set.

By keeping the tools separate we give developers and operators two different tools. Sometimes you need a hammer, and sometimes a screwdriver will do.

This page compares the two: http://www.consul.io/intro/vs/serf.html