gem install passenger passenger start no preference panes to install. No Apache configuration files to update. And Passenger eliminates the need to edit /etc/hosts. To get a Rack app running, just type a single command.
I'm a huge passenger fan, but I should note that: * this is also a single command to get a rack app running once you have it installed * you can easily support multiple ruby versions/gemsets (otherwise you'd need to install/compile passenger for each) * appname.dev is easier than remembering which port all of your rails apps are running on. * you don't have to start each app manually each time.
* Passenger supports using various gemsets very easily using the setup_load_paths.rb file in the config of your app (though multiple ruby versions still seem to be a problem).
* If you're using passenger, why do you have each app running on a different port? Using the Passenger Prefs Pane makes it trivially easy to have each app at its own appname.local URL (though, admittedly, installing an extra prefs pane, where Pow has it built in, gives bonus points to the latter).
* Same with my last point. Passenger automatically handles the booting up or apps when you access their URL in the browser, just like Pow does. Of course, I'm guessing you don't have Passenger installed this way if each app has to run on a different port.