LuaGravity is a reactive language that implements the synchronous approach for concurrency. It is roughly based on Esterel and FrTime, two synchronous languages, the former having an imperative style, the latter being functional.
http://fsantanna.github.io/luagravity/
Unpack LuaGravity to somewhere in your LUA_PATH, and run the tests:
# cd /somewhere_in_lua_path
# tar xvzf luagravity-0.6.1.tgz
# mv luagravity-0.6.1/ luagravity/
# cd luagravity/tests
# make