Ask HN: What would you use to build a Tinder back end?

Starting a side project to play around with some new tech stacks. Recommendations please on what will be best to build the recommendation algorithms for Tinder?

I've built a tinder-like app using rails on the back end. It was very straightforward. In my case, a "user" would like an "item". Users had many Items, and vice versa. The two were related by "line_items".