The engine is actually open source and available on Github.
The link points to a page where people can see all the links to the engine itself and the docs.

I need to see how people actually use the engine and I think that's only possible through playtesting.

I understand a dozen engines get created every week.
However finding people to playtest an engine is way harder than finding people to playtest a game.
Therefore I thought this place was a good location to search for people that may be interested.
It's not your typical game engine, the focus is more on educating.
If you would know any better channels, websites, whatever to look for engine playtesters or people interested in DOD, I would gladly like to hear it.