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Yes, strong mode and the Dart analyzer are all available in the Dart SDK. (Strong mode is in development, but it's still quite useful.)

Yes, but do we also get the custom IDE and whatnot? I'd really like to play with Dart, but I hope it isn't a dead-end for non-Google projects.

Yes we get all of the whatnots ;)

The developers on this project are using Atom https://github.com/atom/atom/ for their day to day Dart development. They are contributing to the Dart plugin https://github.com/dart-atom/dartlang, and implementing a Flutter specific plugin https://github.com/flutter/atom-flutter-dev. The Dart SDK https://github.com/dart-lang/sdk provides the basic source code analysis tools. All of these projects are open source, on github, and see regular commits.