Pow is a zero-configuration Rack server for Mac OS X. It makes developing Rails and Rack applications as frictionless as possible.

Pow is a clean, self-contained server that runs as your user without root privileges. No mucking around with /etc/hosts, no compiling Apache modules, no editing configuration files or installing preference panes. A single command installs and upgrades Pow automatically and your system files are left pristine and untouched.

Running multiple apps with multiple versions of Ruby is trivial. Pow runs as your user on an unprivileged port, and includes both an HTTP and a DNS server.