If we just count stars on GitHub, then Consul is probably the most popular HashiCorp tool. It's one of the few service discovery tools on the market and probably the only one that can be considered modern. The closest alternatives are ZooKeeper and etcd. ZooKeeper is known for being hard to set up and maintain and for being kind of too slow (written in Java) and old already (and you don't want to use anything older than few years these days, do you?). The etcd, though, is a very popular choice, lacks most of the features required for service discovery, and is just a storage rather than a complete solution.
Consul is both service discovery tool and a key/value storage. You need to install Consul agent on each node in order to get it working. As Consul is written in Go, the installation is not very complex: drop the binary and few configuration...
