We at ModCloth have been for a while focused on sharing some of the code we've written with the community, to give back to the open source.
MC-Settings is a cute little gem that provides smart ways of managing your multi-platform/per-deployment application configuration in a convenient set of YAML files, which are easily managed and activated using Capistrano.
For example, beyond configuration that is specific to Rails environment (such as production, development, etc), you may have configuration that is machine specific, or a cluster specific, etc. For example, if you run on multiple clusters, application servers on one cluster may need to use one set of MemCached servers, while your second cluster could have another set. How do you manage configuration in your deployments in such a way that allows sensible defaults, and per-system, cluster, environment overrides?
This is where MC-Settings gem comes in. Read up below on how to use the gem, and typical patterns that work with Capistrano.
Gem Source: https://github.com/modcloth/mc-settings
Update, June 2012While mc-settings is certainly great, it turns out this well maintained gem does very similar thing, but provides more flexibility: