I am already in the process of developing such a framework in R5RS (+ SRFI-0) Scheme born out of my endless frustration with Ruby on Rails.
I should also have pointed out that some of the core choices relating to code re-use in Rails must necessarily look very different in RnRS Scheme, which generally does not support the Inheritance pattern of code reuse. The Delegation and Composition reuse patterns are much more in line with Scheme semantics (and are strictly more expressive according to a paper I vaguely recall from OOPSLA '94 or thereabouts). If you really have an attachment to Inheritance (as in Rails), I suspect that you will find CL more suited to your tastes as OOP was pretty much invented by those guys.
david rush
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