It got opensourced a while ago. But it has been some-what abandoned. GitHub - volfin/mcs
read this, the last comments talk about the situation. [Released] Morph Character System (MCS) - Male and Female page-74
As for now, mcs opensource is incompatible with Unity 2019. I haven’t tested it myself but some guy said is only compatible with Unity 2018 and below.
If you want a character creator tool, there is Makehuman (totally free), Daz3d (freemium), Fuse (free for now) and yeah, those are the best that are compatible with Unity.
Peace.