A basic characteristic of Ragnarok is the use of co-routines. These co-routines are implemented with delimited continuations. There are no OS/kernel controlled threads, like pthread, for scheduling request-handlers in Ragnarok. All the tasks are scheduled by a userland scheduler. And the task is nothing but just a special continuation. The key difference between this and a regular full-stack continuation, is that you can set limits with precision, instead of having to capture the whole stack.
For researchers, there is a paper published on ICFP Scheme Workshop 2016 conference to explain the principle and the design of GNU Artanis:
Multi-purpose web framework design based on websockets over HTTP Gateway.
(to be continued …)