RubyAMF has a lot of dependencies on Rails and it's not based on Rack
either, so it's probably not the best solution for a simple AMF
service. If you don't want to make any modifications, rack-amf (http://
github.com/warhammerkid/rack-amf) is probably going to be the easiest
to integrate. If you're using ActiveRecord though, you're going to
want either RubyAMF or rails3-amf, because sending ActiveRecord
objects over AMF requires some special handling.
Stephen