What are the tools and concepts to achieve real-time recommendations?

I am trying to build a real-time recommender system for my side project. Ideally I am looking for a relatively easy to build and cost effective solution. I am not looking for a state-of-the-art implementation. Nonetheless the solution should be real-time, so if new content comes in, the system should be able to recommend it to people right away. Please give me some tips/resources. Currently Neo4j seems like a good option because it's a graph database and capable to do real-time recommendations, but their product is not free for commercial use.