Firefox’s Pocket recommendations took a good approach. The browser downloads a big daily file with “potential recommendations”, then filters it at the client side.

The big downside was that, because it was turned on by default, a whole bunch of people who didn’t actually want it had it foisted upon them, so it got a very bad reputation right out the gate. Right algorithm, bad execution.

I actually really like Pocket's recommendations, but yeah, the way it's all forced on you it's basically an ad. That's pretty much why I feel like I have to boycott it despite liking the product. It's such a Mozilla move to take something nice and turn it bad for no good reason.

At inception it was just a website that redirected you. There are variations of this created all the time but centered around essays and journalism. It would be trivial to create what is basically a glorified copy of SU, but no one cares enough to do it. Or more accurately, they already exist and we collectively don't care enough to notice.