Jocly is one such program available on GitHub. It is a gaming platform for use on websites through a web browser, or running on your own PC through JoclyBoard. It is mainly a user interface, but is designed in such a way that it can easily extended with new games, with already a lot of supports for the tasks most chess variants have in common. So you would only have to program the part that is unique to your variant, in JavaScript.
We have a version of Jocly installed on CVP, and there is also one on my website, where people could browse to, and play the games they support.
And I do hope, one day, to get some of my simpler variants on there.
And I do hope, one day, to get some of my simpler variants on there.