I've found that the threshold between beginner -> employable is really fuzzy and that's a bit frustrating.
These are still subjective qualifiers though. Useful for who? Useable by which audience? I can easily do both given no other constraints (especially ignoring time). Useful and usable, but never used because chances are someone's done it better and there's no reason to reinvent the wheel.
Other answers I've received have piled additional frameworks or languages on top of what I already know, or suggest specific projects that encompass a wide range of requirements.