Pingable is a Rack handler that let an app respond to a path /ping, with pluggable checks.

Pinion is a Rack application that you can use to compile and serve assets (such as Javascript and CSS).

Pistachio provides a simple HTTP long polling middleware for Rack which is backed by the Stash gem

A doorman for your Rack application. Checks if REMOTE_USER matches the subdomain. Requires some authentication means to set REMOTE_USER.

Minimal server for Rack apps based in EventMachine and http-parser

Pup is a rack based ruby web framework for developing web applications with ease

Pubsubstub can be added to a rack Application or deployed standalone. It uses Redis to do the Pub/Sub

Upload files to Rackspace Cloud or Amazon S3 by URL or file with automatic image resizing.

A library to turn JSON into POROs in a somewhat typesafe manner.

This gem makes it easier to start a Puma server that will bind to a dynamic free port by default and provide helper methods like get and post, managing sessions automatically and using keep-alive to make the requests faster. Usually the server would be run when the test suite starts.

Rails currently returns HTML 500 responses when sent unparsable XML and JSON and gives no way to rescue and handle it

Simple sinatra Rack application that allowes to run sql queries from a web page. Usable for administrative tasks.

A series of components for implementing the Ext.Direct API specification in Rails 2.3 and higher. Ext.Direct in Rails is implementede with Rack Middleware.

Enforces Rails relative URL root at the Rack level, i.e. before requests reach Rails.

The elegance of Rack with none of the unreliability of HTTP

Easy and simple way to package up your rack based application into a .rap (Ruby Application Package) for deployment to a web container that supports .rap such as ThunderCat.

Enable server sent events with rack middleware implemented over Faye and Broadcaster (Redis Pub/Sub)

A rack application daemon that creates an iCal subscription file from exchange calendars.

Implements a Linked Data Platform domain model, Rack middleware for server implementers, and a simple Sinatra-based server for RDF.rb

A bare-bones Ruby HTTP server that talks Rack and uses a thread per connection model of concurrency.