The Nintendo Entertainment System: NES Classic Edition / Nintendo Classic Mini: Nintendo Entertainment System has been around for a little while, is still no doubt loved by its owners and is still tricky to find in stock. Of course, as it's a game console it's also had modders and hackers having a go at getting into the back-end to add more games; it seems that they've now succeeded.
There seem to have been two breakthroughs at a similar time, one out of Japan and one out of Russia, which is nice and contemporary if nothing else. There's a subreddit for modding the NES Mini - because of course there is - and the solution from the Russian hacker seems to be more readily adopted. Having delved off into the murky world of links to find instructions and so on, it certainly seems to be a fiddly process and one with a high risk of upsetting the hardware itself.
A video is also doing the rounds showing the mod in action, which appears to be legitimate in light of the evidence that the hack does indeed seem to exist.
Amazingly, the creator of that video is trying to sell units that have been modded on eBay, so Nintendo's no doubt going to shut that down rather quickly.
It was inevitable that this would happen, ultimately, and it does make us wish that the system had an eShop of its own. We'd have happily spent more money to buy additional games if that had been an option, but instead we're left with the default 30 forever more.
In any case, hacks like this are rather mischievous and certainly not recommended.