Colossus is a lightweight framework for building high-performance applications in Scala that require non-blocking network I/O. In particular Colossus is focused on low-latency stateless microservices where often the service is little more than an abstraction over a database and/or cache. For this use case, Colossus aims to maximize performance while keeping the interface clean and concise.
Applications are built around a set of single-threaded event loops which handle the low-level network interactions, but these event loops are themselves actors which can send and receive messages. The result is an environment where you are able to write low-level event-handling code directly in the event loop, but move other parts into actors with ease.