Garry's Mod is a sandbox game that you can do whatever you want in, and the steam workshop helps out with that! Build stuff, shoot stuff, explode stuff, etc. I'd recommend it.

Hydroneer is a sandbox game that I sadly had to uninstall for another game that I bought. It's a game that you mine dirt and sell the stuff for money, and etc. It's a good game and I'd recommend.

TF2, it's a game most people play on steam. This is a review for the people that haven't. So TF2 is a good game, yet hasn't gotten a major update since 2017's Jungle Inferno. I'd recommend it.