The Missing Gem!
Rails-footnotes by Roman V. Babenko provides you with an easy way to debug your application from the browser. With a small CSS trick the gem displays information such as sessions, request parameters, cookies, filter chain, routes, queries, etc. in the bottom of your browser.
Why the “Missing Gem”? Well frameworks such as symfony have always had this feature. For my $0.02 this should always have been part of rails.
Thanks Roman for what must be one of the most important development gems for rails.