For my current project, I need to do a lot of development in both Ruby (small utilities, database, text utilities, Rails) and back end Common Lisp AI processes. After decades of building custom socket interfaces, CORBA, SOAP, JMS, etc. the simplicity of REST is just right for most of what I need to do that consists of stateless service requests. REST services can return plain text, JSON, XML, etc., depending on what makes sense for any given service.
Implementing Ruby REST clients is simple (what isn't in Ruby :-), and writing generic REST services in Lisp is simple enough using any of the common Lisp web servers (I use Portable AllegroServe, but any that you like will do).