They did tons of open tech interviews for basically anyone who could pass an online quiz, and if they thought they found a good candidate Triplebyte would provide them as higher quality / prescreened candidates to other tech companies looking to make a hire (for a recruiting fee).

I got my first job through Triplebyte actually. I think I would have gotten one without it since I was getting interviews and getting better at them. Even though I had passed the Triplebyte tech screen I got very few company "matches" or opportunities through them, but one ended up working out for me to get my foot in the door.

I recall that they were on HN previously: https://news.ycombinator.com/item?id=23279837 (I haven't looked at their service and don't have plans to.)