This is not a game, but I guess it fits here. ZBrush Core Mini is a free introductory level program for 3D art.
To be more precise, it is a free minimal version of ZBrush, a modeling program designed for sculpting 3D models. The free program allows you to export your work in OBJ format for 3d printing or further processing in other programs.
https://zbrushcore.com/mini/features.php
It is available for Windows and MacOS. System requirements are at the end of the features page (you can get started without a pen tablet). Downloading requires creating an account with an e-mail address and a name. The field for phone number is optional and they didn't badger me for not providing it at all. They don't ask for any payment methods either, as long as you don't want to purchase anything.
There probably are some restrictions on using your creations commercially. You'd have to read the EULA more carefully than I did to know this, since this isn't at present an important consideration for me.
(I should also mention that Blender is free, under active open source development and has 3D sculpting features too. It's good to compare software packages to find what suits your needs.)
[Last edited by Pekka at 06-14-2020 12:48 PM : rewrote parts to be more specific]