Dart
I have followed Dart from the corner of my eye since the inception - after all, Lars Bak), one of the creators is a very well known man in the Smalltalk/Self/OO world, so it had to be interesting!
In the beginning Dart lived a life away from the spotlight, trying to become a “better Javascript” sure is an impossible fight to pick. But with the birth of Flutter and the hard work to make Dart mature over the years, including moving to Dart 2.0 with a sound static type system that actually “feels nice” even for a Smalltalker - Dart is now an extremely interesting platform.
At work I am betting hard on Dart, not only for mobile apps via Flutter, but also server side using Aqueduct and a slew of other packages.