jsPsych is our system of choice for building online experiments. It is moderately easy to learn, especially for people with some programming experience and can be used for experiments of arbitrary complexity.
There is a little tutorial that focuses on usage of jsPsych for Radboud students and employees. It explains how to use jsPsych with the Radcloud Mini data storage. It is not a replacement for the jsPsych totorials.
There are several places where people share their (jsPsych) experiments online: