Concurrency. MenTaLguY shows five ways to do concurrency in Ruby: mutexes, futures, STM, actors and joins.
ActiveLDAP ActiveLDAP gives you an ActiveRecord-like access to LDAP servers.
Ruby in the Enterprise. Timothy M. O'Brien has a great write up on Bringing Rails to the Enterprise. He presents some of the myths, and the reality of using Rails in the field.
ActiveSpec Luke Redpath brings us ActiveSpec, a framework for writing specifications. Looks similar to RSpec, but ActiveSpec deals with generic specification that can be used for test, just as well as validation and selecting from collections. Besides the multiple uses, ActiveSpec allows you to keep your specifications inside the model (a la Rails validation), but also reuse validations across several models. And check the teaser at the end of the post: using specifications with ActiveRecord find methods.
IntelliR JetBrains adds Ruby support to IntelliJ. Watch the screencast.