Rack provides a minimal interface between webservers supporting Ruby and Ruby frameworks.
I recently went through setting up syntax highlighting on Nesta for this site. I started with "Setting up rack-codehighlighter" from the Nesta site, but wasn't loving what Coderay had to offer. Looking at 'rack-codehighlighter' and it's other formatter options and decided to use Ultraviolet.
While this is geared towards Nesta, this will also work for all Rack applications, especially those built on Sinatra.
I was recently working on a project to build continuous integration performance tests on an application which makes extensive HTTP based calls to a middleware application. I was running in to issues where the middleware calls were unstable in the test, stage and load test environments. For the purpose of these tests, I was only interested in the render times of the Rails calls. The obvious choice seemed to cache the external HTTP requests.
I was looking for a simple way to detect mobile devices for this blog, a Sinatra application, and found rack-mobile-detect.