Just remembered and wanted to point out:
async-capable library is executor agnostic, you can use
LocalPool as an executor.
In practice, though, right now futures-0.3 experimentation is mostly assuming tokio is available. I expect that as the ecosystem matures, there will arrive a lighter "runtime" over mio to fill the niche of clients that really only need
LocalPool and don't need the full tokio runtime.
(That said, there is some worth to "just using tokio", so long as you can fit it into your trust model.)
(Also, executor/reactor/runtime all of these futures bits I don't know the exact separation of concerns forgive me)