You can use OpenSesame, jsPsych, lab.js - or write your own experiment in JavaScipt/HTML/CSS. Get participants from Prolific or MTurk (or from wherever).
Be in charge of your data
JATOS is free and open source. You can install JATOS on your own server (at your university) - or in the cloud - wherever you want.
JATOS on MindProbe
Use this free JATOS sponsored by the European Society for Cognitive Psychology (ESCoP) with Journal of Cognition as their official journal and OpenSesame.