by is a library preloader for ruby designed to speed up process startup. It uses a client/server approach, where the server loads the libraries and listens on a UNIX socket, and the client connects to that socket to run processes. For each client connection, the server forks a worker process, which uses the current directory, stdin, stdout, stderr, and environment of the client process. The worker process then processes the arguments provided by the client. The client process waits until the worker process closes the socket, which the worker process attempts to do right before it exits.