I wouldn't say this is a call to free labor. It would be if you were asked to port an existing unsupported language to repl.it (which is how I read it at first). However, this is a contest to reward building your own totally new language (which presumably you were going to do anyways) at least, for some segment of time, on repl.it. I suppose it could be seen as debugging repl.it for free, because this endeavor is likely to break repl.it in so many unforseeable ways.