Lightning

Lightning is an HTTP Server and TCP Client/Server framework written in Swift and inspired by Node.js. It runs on both OS X and Linux. Like Node.js, Lightning uses an event-driven, non-blocking I/O model. In the same way that Node.js uses libuv to implement this model, Lightning uses libdispatch.

This makes Lightning fast, efficient, and most crutially single-threaded by default. You simply do not need to worry about locks/mutexes/semaphores/etc if you have server-side state. Of course, Lightning applications can make use of libdispatch to easily offload heavy processing to a background thread if necessary.