CoffeeScript is deliberately tied to JavaScript by design. Porting it to work with Erlang or C would be rather awkward. Outside the context of a JavaScript environment, CoffeeScript doesn't seem to offer enough benefits over, say, Python to be worth the massive amount of work this would entail. If you mean you want another language that can interact with Erlang or C code, those already exist (in fact, there are a lot of langauges that are C-compatible since it's the lingua franca of modern computing).
By “CoffeeScript for C“, I think Onr means not supporting all of CoffeeScript’s features in C, but rather making a language that is very much like C, but better. So CoffeeScript for C wouldn’t try to implement `@foo` to mean `this.foo`, since there is no `this` in C. Rather, it would look at the common idioms in C that are more verbose than they need to be and shorten them.
CoffeeScript for C would probably use semantic whitespace, like normal CoffeeScript. Maybe it would make writing types easier – it would support a syntax for types that doesn’t require the use of http://www.cdecl.org/. It would still try to be “just C”, so it wouldn’t support much higher-level features like function closures.
And if you want an alternative Erlang, see Elixir (http://elixir-lang.org/), Joxa (http://joxa.org/) and LFE (https://github.com/rvirding/lfe).