[bjourne]

If you want something that scales, I believe you have to build it yourself. A recommendation system personalized for each user and adapting to feedback in real-time is very resource intensive. The problem is that for the recommendation system to be fast and adaptive, it needs tight integration with your database(s) which is hard for prebuilt solutions to afford.

Fortunately, building a recommendation system is not that hard. Google and read up on postgresql's ts_vectors and refresh your linear algebra. You probably will have to make some trade-offs; the more personalized the recommendations, the less likely it is to scale well.

Note: It was over seven years since I worked with a recommendation system. The prebuilt solutions might have improved since then.