This is the back-end for Treadmill, an environment for interacting with Gerbil in Emacs.
Typically, you will install this package via gxpkg install github.com/thunknyc/gerbil-treadmill and then connect to Gerbil via M-x treadmill-spawn from within Emacs. However, if you want to run your own Gerbil network REPL, you can connect to it via M-x treadmill-connect.