Not quite. The futures crate, version 0.1, contained a definition of the `Future` trait and a bunch of the combinator methods. This was iterated on a lot. Eventually, the bare minimum traits were added to the standard library.

The futures crate, version 0.3 (released under the name `futures-preview` right now with an alpha version number), contains the helper methods for the standard library's trait.

No; it re-exports the standard futures. Its purpose is two-fold: one, it's where futures were experimented with before they got into std, and two, it's where extra functionality can live. We only put what was absolutely necessary into std.