temp.rb

module Reportable
  def as_json
    {:meta => meta, :report => report}
  end
end

class ReportPresenter
  include Reportable
  def self.column(name, options={})
  end

  def meta
    #...prepare meta
  end

  def report
    # prepare report based on columns
  end
end

class SoftwareOverviewPresenter < ReportPresenter
  column :application, :model => Applications, :column => :name
  column :publisher, :from => :application, :path => "publisher.name"
  column :used, :from => lambda {}
end

class OrganizationalUnitTagCloudPresenter
  def as_json
    #...
  end
end

class CombinationPresenter
  def initialize(*items)
    @items = items
  end

  def as_json
    @items.each_with_object({}) { |item, res| res.merge(item.as_json) }
  end
end

# in sinatra app
get 'report' do
  report = company.reports.software_overview(query)
  ous = OrganizationalUnitTagCloudPresenter.new company.ous

  app.combine(report, ous)
end

I like the base presenter class for report. I'd nix the Reportable module given it's tightly dependent on the presenter directly though. I'm still undecided on the column stuff and worry that you may need some sort of setup that might make the column method a bit more complex than a PORO. That being said, having a base class to deal with sorting, pagination, and filtering makes perfect sense.

For the sinatra app portion, I like having the idea of a 1:1 mapping between the report identifier and a presenter... if that presenter wants to delegate to a presenter internally, it's free to do so (as in the case for OU) but having the sinatra be a very simple dispatcher where it just needs to resolve the report and hand it the request context seems better.