Gqtp gem provides both GQTP client, GQTP server and GQTP proxy implementations. They provide asynchronous API. You can use gqtp gem for high concurrency use.
Groonga-client gem supports HTTP or [GQTP (Groonga Query Transfer Protocol)](http://groonga.org/docs/spec/gqtp.html) as the protocol using a client.
Groonga command line clients can work without Groonga. `groonga` command provided by Groonga can only use for GQTP but they can use for both GQTP and HTTP.