I assume you mean battle-tested from a security standpoint. I suppose you'd need to make that judgment call yourself. In my opinion, many of the options I lis

I assume you mean battle-tested from a security standpoint. I suppose you'd need to make that judgment call yourself. In my opinion, many of the options I listed have seen sufficient production usage that I consider them roughly as secure as any mainstream framework. For example, Play and Scalatra are used at Netflix, BBC, LinkedIn, etc. Many expressly avoid notoriously dangerous (and frankly alarming) deserialize-user-input-and-execute patterns, which is in my experience the most common form of framework vulnerability. As for performance, scalability, and reliability under pressure, that is precisely the point I was making earlier: higher-performance platforms combined with frameworks designed for performance and scalability are targeting grace under pressure moreso than legacy frameworks. Higher performance gives you greater peace of mind with availability, responsiveness, and user experience.