Unfortunately, the lack of posted license means nobody is permitted to use it without getting explicit permission. I really doubt that was the intent of the author, though.
That's not really true, of course. IP law isn't a physical law, so if your conscience is clear and you accept the risks, you're permitted to do whatever seems needful or fun. The only "risk" here is the author suing you, and by my estimate (that risk) * (potential damages) is a really really tiny number.
I've used lots of projects on github that aren't formally licensed and I intend to continue to do so, and I would guarantee through money bets that any negative consequences will be overwhelmingly outweighed by the benefits. And to be clear, I expect negative consequences to be precisely zero.
Incidentally, the licensing culture that's sprung up in the wake of the open source movement is pretentious and self-righteous. It claims that everywhere is deathly threats and that we need to build up a bulwark of legal defenses to protect us from the ever present dreadnaughts of closed-sourcedness, that we must be adhere to a prissy and ultraconservative standard of conduct in hacker circles to be vigilant against the enemy. But that's dumb. People are mostly good.
More, it's smugly eager to defend its place as the champion and one true defender of open source and, in doing so, often trades reasonableness for silliness when it thinks reasonableness threatens its stature.
My favorite example is when I came across an open source license proponent[1] who insisted that declaring your work public domain is worse than using a license, even though it's clearly just as good (actually, better). The claim against public domain is that some jurisdictions don't have it as a concept, which neglects the fact that the vast majority of active developers are in jurisdictions that do, and that it's extremely unlikely that anyone in one of these rare ambiguous jurisdictions will benefit from violation, or care to, or be able to materially or spiritually harm the original author in any way.
And, no, I don't think vanishingly likely technically possible scenarios matter. Public domain is clear and obvious, and that's a big benefit. No matter how permissive the license, you immediately make someone have to care and possibly look up the license terms. Moreover, you continue to reinforce the notion that the forces behind the most common open source licenses are mostly right, when they aren't. A perfectly legitimate way to open source software, public domain, existed long before they did and it doesn't carry with it the tacky stain of anti-competitive, anti-corporate smearing.
[1] I've come to find out that this is license proponents' standard argument.
