The first alpha versions of Mathics3 were done in 2011 by Jan Pöschko. He worked on it for a couple of years to about the v0.5 release in 2012. By then, it had 386 built-in symbols. Currently there are over a 1,000, and even more when Mathics3 modules are included.
After that, Angus Griffith took over primary leadership and rewrote the parser to pretty much the stage it is in now. He and later Ben Jones worked on it from 2013 to about 2017 to the v1.0 release. Towards the end of this period, Bernhard Liebl worked on this, mostly focused on graphics.
A docker image of the v.9 release can be found on dockerhub.
Around 2017, the project was largely abandoned in its largely Python 2.7 state, with some support for Python 3.2-3.5 via six.
Subsequently, around mid 2020, it was picked up by the current developers. A list of authors and contributors can be found in the