All of the servers listed here are standalone servers, while Passenger is a module for existing servers. I don't really see why you couldn't include Passenger here, but it seems like they're only comparing like to like, which I guess is fair.
You can use Passenger as a standalone server too, it's called Passenger Standalone. You can install it with 'gem install passenger', and run it by running 'passenger start'.
Oh, so you can. I actually went and checked the Passenger site to see if my information was current since I mainly use Puma these days, but I didn't scroll down far enough to see the standalone version.
But installing it as a module still seems to be the recommended method, so I can see still see why it isn't included in a list of servers that are meant to be proxied to.
