Important warning: You should be aware when using fibers with Rails that you can get a stack overflow error if your stack grows bigger than 4Kb (which is enough for most things though), this got even worse with the 3.1 release in which you can easily overflow the stack, here is an example here. Simple async demo stack with Rails 3.1 + EventMachine and Fibers. Hit localhost:3000/widgets to do a 1s