Decorum is a Ruby gem providing general purpose Decorator/Chain of Responsibility behavior for any Ruby object. It is very small and has no requirements outside of the standard library. Decorum is relased under the MIT license. Use it wherever.
Apply is the grant management system of the Public Programs Office at the American Library Association. It is written in Ruby/Rails, (~14K LOC minus templates, tests, etc.) and has over 7,500 registered users. The codebase is not (yet) open, but this blog contains a number of in-depth notes in its design.
Please note that the following two projects are somewhere between "code spike" and "not nearly ready for production." But there are some interesting ideas.
As in "urbs in horto"---like Chicago, Urbs is run by the machine.Urbs is an experiment in using a state machine to regulate the HTTP request/response cycle to (a) ensure valid responses and (b) present a cleaner, more orthogonal approach to application developers by firmly separating request handling and presentation, representing each as a simple, distinct developer task. Read more at GitHub.
Urbivore is the Urbs structured logger and asynchronous work manager. (It is in a slightly more usable state than Urbs itself, but you've still been warned.) It has a number of nice features, including: