It's a simulator of a dataflow machine.

First, you define a dataflow graph and save it to test.dfg:

recv :start do
  send :sum, :a, 10
  send :sum, :b, 15
end
recv :sum do |a, b|
  send :mul, :x, (a+b)
end
recv :mul do |x|
  send :stop, :x, x
end

This is a Ruby dialect.