It looks like it builds on those resources, but lets you deal with them via a simple dotenv-style file, rather than full YAML. Could be helpful for integration with those kinds of files or if you're migrating from an older .profile-based config.
This was prompted largely by a move from Docker Compose, where we used env_file quite a bit. kenv will both create the Secret/ConfigMap resource as well as inject the env lookups into an existing Kubernetes resource (deployment, replicaset, daemonset, or replication controller). This allows us to keep our environment specific configuration alongside the app and just inject at deploy time.