[thristian]

Just the first difference that caught my eye: section 3.1 of the document you linked to says that once fulfilled or rejected, a Promise must not change to any other state, and its value may not change. In Guido's exposition of Deferreds, under the heading "Idea 2: Pass results from callback to callback", he says:

The most interesting bits are the last two lines: the result of each callback is passed to the next. This is different from how things work in concurrent.futures and Tulip, where the result (once set) is fixed as an attribute of the Future. Here the result can be modified by each callback.

This enables a new pattern when one function returning a Deferred calls another one and transforms its result, and this is what earns this idea three stars.