It’s funny how every Rails application I - and possibly you - work on ends up needing some sort of per-environment global constants.
Examples may include the application url - It might be used in account activation emails and thus should be different between the development and production environments.
Or perhaps your application depends on external services that, depending on the environment, are available in different URIs.
There are a couple solutions out there but my needs were simple and straightforward, thus I developed a small rails plugin that is the simplest thing that could possibly work: AppConstants.
It's been useful for my current project and I hope it can be useful to someone else too ;)