Friends of _magpie
If _magpie is not your taste, there are great alternatives. Check them out to see what’s best for you.
PsiTurk
psiTurk is a great platform for developing and running online experiments with Amazon’s MechanicalTurk. _magpie is heavily inspired by psiTurk, but developed a life of its own because psiTurk is not as flexible (being tied to MTurk) and portable (requiring researchers to view your experiment through a python application). On the other hand, psiTurk is the basis for Dallinger which provides a mind-blowing framework for running difficult experimental designs with multiple participants or chains of dependent experiments (such as in cultural evolution experiments).
LabVanced
LabVanced is a good choice for those who prefer to develop experiments using a graphical user interface. No coding is required and the experiment designer runs directly in the browser. Designed to accommodate psychological studies, market research, recruitment tests and e-Learning, LabVanced offers an extensive library of templates to build upon. You can use the in-house crowdsourcing solution or link your experiment to others such as MechanicalTurk. As of 2018, the alpha version can be used free-of-charge.
Ibex & Ibex Farm
Ibex makes it particularly easy to realize psycholinguistic experiments, like self-paced reading tasks. You can install your own server app or you can use Ibex Farm. To use Ibex Farm, you simply need to upload a file with information about your trials in the right formatting and you are good to go. This is exceptionally useful as long as what you want to realize falls within the scope of experiments Ibex is designed for.