It's been a few months since we last saw any activity on the No Man's Sky front, when Hello Games released the 1.22 patch that brought "exocraft" buggies to every planet in the galaxy. But it appears that something new, and potentially big, is in the works. Reddit mods have been receiving packages from the studio since late last week containing NMS merchandise of various sorts and a single, numbered audio cassette, each of them carrying a hidden message.
There are apparently 16 audio tapes in all, and they're very slowly being uploaded to the net for examination—not all of them have been received yet, and as NeoGAF user legacyzero pointed out in his summary of events so far, "Nobody owns a goddamn cassette player." Another problem, as seen in these captures of Discord chats, is that some users don't want to share what they've received, although one of them claimed that Hello Games said it "expected this to happen and will help us out when needs be."
So at this point it's impossible to say what information they will collectively contain, but spectrographic analyses of two of the recordings have revealed the same set of characters on both: 706s7274616p. Run that through an ROT13 converter and you end up with a proper hexadecimal string, 706f7274616c, which when converted to ASCII leaves a single word: Portal.
The word is especially portentous in light of a note that came with at least one of the packages: "The giant gateway calls out to me, filling my mind with whispered secrets of a far-flung world." That's actually a line from the game, and also an allusion to the portals that appear on certain planets that, to this point, nobody has been able to figure out how to operate.
It seems fairly clear that whatever is going on here—if there is in fact something happening at all—is somehow related to those structures. Passageways to exciting new planets, or even an entirely different galaxy, possibly one more in line with initial player expectations? Perhaps it will work the other way, and we'll have strange new visitors coming to us. Or it could be something much more mundane, which I'd guess is the most likely outcome—a way to meet other intergalactic explorers, maybe.
I've emailed Hello Games for more information, and will update if and when I receive it. For now, you can keep up with the unfolding mystery in the Cassettes Megathread.