There is https://www.serf.io/ which is a Hashicorp project as well, but the license doesn't seem as bad as nomad and from what I understand it's the basis for things like nomad and consul.
Serf is used within Consul for agent to agent checks (and some communication). There's an entire subsystem called the 'serf check' that shows up within every single Consul agent. It's one component of the entire 'Consul' system.
IIRC Serf is mostly a library; I think the product around it is more for demonstration than actual expected use. Consul uses libserf for it's gossip protocol.
Learned about it in this blog post: https://fly.io/blog/building-clusters-with-serf/