multiple runtimes being used together successfully

[nikomatsakis]

Brief summary

There are many difference scenarios when you might want to have multiple runtimes working together. We could use more stories about that!

We do have:

• Alan has an external event loop and wants to use futures/streams, a story about integration with cocoa
• Actix QT blog post, could be a good source for a story

Optional details

• (Optional) Which character(s) would be the best fit and why?
  • Alan: the experienced "GC'd language" developer, new to Rust
  • Grace: the systems programming expert, new to Rust
  • Niklaus: new programmer from an unconventional background
  • Barbara: the experienced Rust developer
• (Optional) Which project(s) would be the best fit and why?
  • List some projects here.
• (Optional) What are the key points or morals to emphasize?
  • Write some morals here.