Dart is an open-source, scalable, object-oriented programming language, with robust libraries and runtimes, for building web, server, and mobile apps. It was originally developed...
Haxe is an open source toolkit based on a modern, high level, strictly typed programming language, a cross-compiler, a complete cross-platform standard library and ways to access...
Clojure to JS compiler
Develop software on one of the best IDEs anywhere: Pharo, and deploy on the web. In development, but the roadmap has a very inclusive goal.
Ceylon is a language for writing large programs in teams, with a powerful flow-sensitive static type system. It runs on the JVM or in a browser (transpiled to JS).
Smalltalk on the web.
Java (via GWT)
C (via Emscripten)