Looks interesting. Actively developed : https://github.com/githwxi/ATS-Postiats

edit: You are right, I did not know there was a third version. If only this thing had release notes. I have no idea the current state of the language is. Hongwei, if you're listening!

If this language is going to be a thing it needs community development.

It's "very very minorly" (that's the only commit message used) difficult to follow, but I'm pretty sure ATS2 (Postiats) is in maintenance mode (activity is build changes), with ATS3 (Xanadu) https://github.com/githwxi/ATS-Xanadu being the focus of active development.