Most contemporary compile-to-JS languages target the browser, but do not inhabit it. I'm excited about a system that encourages apps and tools to evolve organically together, instead of tools developing separately from applications, which is the status quo.
Other than that, Common Lisp has some really interesting capabilities relative to ClojureScript, and is also fun!
1:http://bitsavers.org/pdf/xerox/interlisp/Interlisp_Reference... section 1.2