On Android, a mobile phone (play store) is an authorized way, on which you can download your favorite 3d games. For PC there are lots of websites available that are ready to serve you a 3d game without any interruption.
Few most wondering and authorized site for downloading 3d games are given below:
gametop.com
freegamepick.net
rockthe3d.com
en.softonic.com
gamebra.com
About every website has an easy way to download 3d games for pcs.